Semiconductor device

ABSTRACT

In order to reduce parasitic inductance of a main circuit in a power supply circuit, a non-insulated DC-DC converter is provided having a circuit in which a power MOS•FET for a high-side switch and a power MOS•FET for a low-side switch are connected in series. In the non-insulated DC-DC converter, the power MOS•FET for the high-side switch is formed by a p channel vertical MOS•FET, and the power MOS•FET for the low-side switch is formed by an n channel vertical MOS•FET. Thus, a semiconductor chip formed with the power MOS•FET for the high-side switch and a semiconductor chip formed with the power MOS•FET for the low-side switch are mounted over the same die pad and electrically connected to each other through the die pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/912,796, filed Oct. 27, 2010, which, in turn, is a continuation ofU.S. application Ser. No. 12/430,972, filed Apr. 28, 2009 (now U.S. Pat.No. 7,852,651), which, in turn is a continuation application of U.S.application Ser. No. 11/863,556, filed Sep. 28, 2007 (now U.S. Pat. No.7,535,741), which, in turn, is a continuation of U.S. application Ser.No. 11/288,103, filed Nov. 29, 2005 (now U.S. Pat. No. 7,295,453), andwhich application claims priority from Japanese patent application No.2004-345798, filed Nov. 30, 2004, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device technique, andparticularly to a technique effective if applied to a semiconductordevice having a power supply circuit.

A DC-DC converter widely used as one example of a power supply circuithas a configuration wherein a high-side power MOS•FET (Metal OxideSemiconductor Field Effect Transistor) and a low-side power MOS•FET areconnected in series. The high-side power MOS•FET has a switch functionfor control of the DC-DC converter, and the low-side power MOS•FET has aswitch function for synchronous rectification. By alternately turningon/off these two power MOS•FETs while synchronization is being achievedtherebetween, the conversion of a power supply voltage is carried out.

Such a DC-DC converter has been descried in, for example, JapaneseUnexamined Patent Publication No. 2003-528449 (patent document 1), whichdiscloses a configuration wherein a high-side power MOS•FET, a low-sidepower MOS•FET, a driver circuit that drives these power MOS•FETs, and aninput capacitor are accommodated within the same package.

A package configuration wherein a high-side power MOS•FET constituting aDC-DC converter is constituted of a horizontal power MOS•FET, a low-sidepower MOS•FET constituting the DC-DC converter is configured of avertical power MOS•FET, and these power MOS•FETs are mounted over acommon frame, has been disclosed in, for example, Japanese UnexaminedPatent Publication No. 2002-217416 (patent document 2).

SUMMARY OF THE INVENTION

Meanwhile, a non-insulated DC-DC converter employed in a power supplycircuit for a desktop personal computer, a server and a game machine orthe like tends to increase in current and frequency with a demand for anincrease in current of a driven CPU (Central Processing Unit) or thelike and miniaturization of passive parts like a choke coil and aninput/output capacitor, etc.

However, a problem arises in that a loss increases due to main circuitinductance parasitic on a main circuit around the input capacitor of thenon-insulated DC-DC converter under the large-current and high-frequencyconditions. In particular, a problem arises in that when the maincircuit inductance parasitic on the main circuit around the inputcapacitor increases with the increases in current and frequency, a leapvoltage at the turning off of the high-side power MOS•FET of the DC-DCconverter increases, thus resulting in an increase in switching loss andthe incurrence of large loss.

The patent document 1 has disclosed such a configuration that asemiconductor chip formed with a high-side power MOS•FET, asemiconductor chip formed with a low-side power MOS•FET, a semiconductorchip formed with a driver circuit, and an input capacitor Cin areaccommodated within the same package. In this case, the source of thehigh-side power MOS•FET is electrically connected to its correspondingwiring of a wiring board through a bonding wire. The wiring iselectrically connected to the drain of the low-side power MOS•FET. Thesource of the low-side power MOS•FET is electrically connected to itscorresponding output wiring of the wiring board through a bonding wire.In such a configuration, however, parasitic inductance cannot be reducedsufficiently because the source of the high-side power MOS•FET an thedrain of the low-side power MOS•FET are connected by the bonding wire.In other words, since they are electrically connected to each other bythe bonding wire, there is a limit to a reduction in parasiticinductance.

The patent document 2 has disclosed such a configuration that thehigh-side power MOS•FET is constituted of the horizontal power MOS•FET,the low-side power MOS•FET is constituted of the vertical power MOS•FET,and these power MOS•FETs are mounted over the common frame. Since theinput capacitor is externally provided in this case, a wiring-to-wiringdistance to each power MOS•FET increases. Since the main circuitinductance parasitic on the main circuit around the input capacitorcannot be reduced sufficiently with the increase in the wiring-to-wiringdistance, voltage conversion efficiency of a semiconductor device isalso reduced. While such a configuration that the input capacitor Cin isaccommodated within the same package as each semiconductor chip, hasbeen disclosed in the patent document 1, a given degree of distanceoccurs between the input capacitor and each power MOS•FET and hence theparasitic inductance cannot be reduced sufficiently and power supplyefficiency of a semiconductor device is lowered.

An object of the present invention is to provide a technique capable ofreducing parasitic inductance of a main circuit in a power supplycircuit.

Another object of the present invention is to provide a techniquecapable of improving power supply efficiency of a semiconductor device.

The above and other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

Representatives of the inventions disclosed in the present applicationwill briefly be explained in summary as follows:

The present invention provides a semiconductor device wherein a fieldeffect transistor of a first semiconductor chip is formed of a p channelvertical field effect transistor, and a field effect transistor of asecond semiconductor chip is formed of an n channel vertical fieldeffect transistor, whereby the first and second semiconductor chips aremounted over the same chip mounting section and electrically connectedto each other.

The present invention provides a semiconductor device wherein a fieldeffect transistor of a first semiconductor chip is formed of a p channelvertical field effect transistor, and a field effect transistor of asecond semiconductor chip is formed of an n channel vertical fieldeffect transistor, whereby the first and second semiconductor chips aremounted over the same chip mounting section and electrically connectedto each other,

wherein a capacitor is provided which is electrically connected betweena first lead plate that electrically connects electrodes of the firstsemiconductor chip to an external terminal for the supply of inputpower, and a second lead plate that electrically connects electrodes ofthe second semiconductor chip to an external terminal for the supply ofa reference potential, and

wherein the capacitor has a pair of electrodes of which the one isbonded to the first lead plate and of which the other is bonded to thesecond lead plate.

Advantageous effects obtained by representatives of the inventionsdisclosed in the present application will briefly be explained asfollows:

A field effect transistor of a first semiconductor chip is formed of a pchannel vertical field effect transistor, and a field effect transistorof a second semiconductor chip is formed of an n channel vertical fieldeffect transistor, whereby the first and second semiconductor chips aremounted over the same chip mounting section and electrically connectedto each other. Thus, since inductance components in a wiring pathbetween the first and second semiconductor chips can be reduced,parasitic inductance of a main circuit in a power supply circuit can bereduced.

A capacitor has a pair of electrodes whose one is bonded to the firstlead plate and whose other is bonded to the second lead plate. Thus,since parasitic inductance of a main circuit in a power supply circuitcan be reduced, power supply efficiency of a semiconductor device can beenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of one example of a semiconductor deviceshowing a first embodiment of the present invention;

FIG. 2 is a timing chart of the semiconductor device shown in FIG. 1;

FIG. 3 is a plan view illustrating the interior of a package discussedby the present inventors;

FIG. 4 is a sectional view taken along line Y1-Y1 of FIG. 3;

FIG. 5 is a plan view showing the interior of a package discussed by thepresent inventors;

FIG. 6 is a sectional view taken along line Y2-Y2 of FIG. 5;

FIG. 7 is a plan view depicting the interior of a package of the patentdocument 2 discussed by the present inventors;

FIG. 8 is a circuit diagram of one example of the semiconductor deviceshowing the first embodiment of the present invention;

FIG. 9 is a plan view illustrating the interior of a package of thesemiconductor device showing the first embodiment of the presentinvention;

FIG. 10 is a sectional view taken along line Y3-Y3 of FIG. 9;

FIG. 11 is an enlarged plan view of a semiconductor chip formed with afield effect transistor for a high-side switch shown in FIG. 9;

FIG. 12 is a fragmentary enlarged plan view of the semiconductor chipshown in FIG. 11;

FIG. 13 is a sectional view taken along line X1-X1 of FIG. 12;

FIG. 14 is a sectional view taken along line Y4-Y4 of FIG. 12;

FIG. 15 is a sectional view taken along line X2-X2 of FIG. 12;

FIG. 16 is a sectional view of a unit transistor cell of a field effecttransistor for a low-side switch in the semiconductor chip shown in FIG.9;

FIG. 17 is a sectional view of a unit transistor cell of a field effecttransistor for a high-side switch in a semiconductor device showing asecond embodiment of the present invention;

FIG. 18 is an overall plan view illustrating a main surface side of apackage of a semiconductor device showing a third embodiment of thepresent invention;

FIG. 19 is a side view of the package shown in FIG. 18;

FIG. 20 is an overall plan view showing a back surface side of thepackage shown in FIG. 18;

FIG. 21 is an overall plan view showing the main surface side of thepackage as seen through the interior of the package shown in FIG. 18;

FIG. 22 is a sectional view taken along line Y5-Y5 of FIG. 21;

FIG. 23 is a sectional view taken along line X3-X3 of FIG. 21;

FIG. 24 is an overall plan view of a semiconductor chip formed with afield effect transistor for a low-side switch in the package shown inFIG. 18;

FIG. 25 is an overall plan view showing a main surface side of a packageof a semiconductor device illustrative of a fourth embodiment of thepresent invention;

FIG. 26 is a sectional view of a unit transistor cell of a semiconductorchip formed with a power MOS•FET for high side in the package shown inFIG. 25;

FIG. 27 is an overall plan view showing a main surface side of a packageof a semiconductor device illustrative of a fifth embodiment of thepresent invention as seen through the interior of the package;

FIG. 28 is a sectional view taken along line Y6-Y6 of FIG. 27;

FIG. 29 is an overall plan view showing an upper surface of a package ofa semiconductor device illustrating a sixth embodiment of the presentinvention;

FIG. 30 is a sectional view taken along line Y6-Y6 of FIG. 29;

FIG. 31 is a sectional view of one example of a configuration wherein aradiating fin is bonded onto the upper surface of the package shown inFIGS. 29 and 30;

FIG. 32 is an overall plan view showing an upper surface of a package ofa semiconductor device illustrating a seventh embodiment of the presentinvention;

FIG. 33 is an overall plan view showing a main surface side of thepackage as seen through the interior of the package shown in FIG. 32;

FIG. 34 is a sectional view taken along lines Y7-Y7 of FIGS. 32 and 33;

FIG. 35 is a partly broken perspective view of one example of an inputcapacitor;

FIG. 36 is a sectional view of a spot corresponding to line Y7-Y7 ofFIG. 32 in a package of a semiconductor device showing an eighthembodiment of the present invention;

FIG. 37 is an overall plan view showing a main surface side of a packageof a semiconductor device illustrating a ninth embodiment of the presentinvention as seen through the interior of the package;

FIG. 38 is a sectional view taken along line Y5-Y5 of FIG. 37;

FIG. 39 is a sectional view taken along line X3-X3 of FIG. 37;

FIG. 40 is an overall plan view showing an upper surface of a package ofa semiconductor device illustrating a tenth embodiment of the presentinvention;

FIG. 41 is a sectional view taken along line Y5-Y5 of FIG. 40;

FIG. 42 is a sectional view taken along line X3-X3 of FIG. 40;

FIG. 43 is a sectional view showing one example of a configurationwherein a radiating fin is bonded onto the upper surface of the packageshown in FIGS. 40 through 42;

FIG. 44 is an overall plan view showing an upper surface of a package ofa semiconductor device illustrative of an eleventh embodiment of thepresent invention;

FIG. 45 is an overall plan view illustrating a main surface side of thepackage as seen through the interior of the package shown in FIG. 44;

FIG. 46 is a sectional view taken along lines Y5-Y5 of FIGS. 44 and 45;

FIG. 47 shows one example of a configuration of a package in which aninput capacitor is contained therein, and is a sectional view of a spotcorresponding to each of lines Y5-Y5 of FIGS. 44 and 45;

FIG. 48 is a plan view showing an example of a mounted state of thepackage or the like of the semiconductor device showing the eleventhembodiment of the present invention;

FIG. 49 is a side view of the package shown in FIG. 48;

FIG. 50 is an explanatory view showing an example of a circuit systemconfiguration of a non-insulated DC-DC converter containing the packageof the semiconductor device showing the eleventh embodiment of thepresent invention;

FIG. 51 is a flow diagram showing a process for assembling thesemiconductor device showing the eleventh embodiment of the presentinvention;

FIG. 52 is a plan view showing a main surface of each unit area of alead frame in the assembly process of the semiconductor device showingthe eleventh embodiment of the present invention;

FIG. 53 is a plan view showing the main surface of the lead framesubsequent to the mounting of a semiconductor chip on each die pad ofthe lead frame shown in FIG. 52;

FIG. 54 is a plan view illustrating the main surface of the lead framesubsequent to the connection of a lead plate onto the semiconductor chipplaced on the lead frame shown in FIG. 53;

FIG. 55 is a plan view showing the main surface of the lead framesubsequent to the performance of wire bonding processing on thesemiconductor chip on the lead frame shown in FIG. 54;

FIG. 56 is a plan view showing the main surface of the lead framesubsequent to the sealing of the semiconductor chip or the like on thelead frame shown in FIG. 55 with an encapsulator;

FIG. 57 is a plan view illustrating the main surface of the packageobtained from the lead frame of FIG. 56 by cutting;

FIG. 58 is an overall plan view showing a main surface side of a packageof a semiconductor device illustrating a twelfth embodiment of thepresent invention as seen through the interior of the package;

FIG. 59 is a sectional view taken along line Y7-Y7 of FIG. 58;

FIG. 60 is a circuit diagram showing the semiconductor device shown inFIG. 58;

FIG. 61 is an overall plan view showing a main surface side of a packageof a semiconductor device illustrative of a thirteenth embodiment of thepresent invention as seen through the interior of the package;

FIG. 62 is a sectional view taken along line Y5-Y5 of FIG. 61;

FIG. 63 is a sectional view showing a package of a semiconductor deviceillustrating a fourteenth embodiment of the present invention;

FIG. 64 is a sectional view illustrating a state in which the packageshown in FIG. 63 is mounted to a wiring board and a radiating fin isattached;

FIG. 65 is a sectional view showing a state in which a package of asemiconductor device illustrative of a fifteenth embodiment of thepresent invention is mounted to a wiring board, and a radiating fin isattached; and

FIG. 66 is a fragmentary plan view of FIG. 65 as viewed from the backsurface of the wiring board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments will be described by being divided into aplurality of sections or embodiments whenever circumstances require itfor convenience in the following embodiments. However, unless otherwisespecified in particular, they are not irrelevant to one another. Onethereof has to do with modifications, details and supplementaryexplanations of some or all of the other. When reference is made to thenumber of elements or the like (including the number of pieces,numerical values, quantity, range, etc.) in the following embodiments,the number thereof is not limited to a specific number and may begreater than or less than or equal to the specific number unlessotherwise specified in particular and definitely limited to the specificnumber in principle. It is also needless to say that components(including element or factor steps, etc.) employed in the followingembodiments are not always essential unless otherwise specified inparticular and considered to be definitely essential in principle.Similarly, when reference is made to the shapes, positional relationsand the like of the components or the like in the following embodiments,they will include ones substantially analogous or similar to theirshapes or the like unless otherwise specified in particular andconsidered not to be definitely so in principle, etc. This is similarlyapplied even to the above-described numerical values and range.Constituent elements each having the same function in all the drawingsfor describing the embodiments are respectively given the same referencenumerals and their repetitive explanations are omitted where possible.Preferred embodiments of the present invention will hereinafter bedescribed in detail based on the accompanying drawings.

First Preferred Embodiment

A semiconductor device according to a first embodiment is anon-insulated DC-DC converter employed in a power supply circuit ofelectronic equipment like, for example, a desktop personal computer, anotebook-size personal computer, a server or a game machine or the like.

FIG. 1 shows one example of a circuit diagram of a non-insulated DC-DCconverter 1 discussed by the present inventors. The non-insulated DC-DCconverter 1 has elements like a control circuit 2, a driver circuit 3,power MOS•FETs (hereinafter abbreviated simply as “power MOS”) QH1 andQL1, an input capacitor Cin, an output capacitor Cout and a coil L, etc.Incidentally, symbol D indicates a drain, and symbol S indicates asource, respectively. Symbols L1 through L6 indicate parasiticinductances which are parasitic on a main circuit of the non-insulatedDC-DC converter.

The control circuit 2 is a circuit like, for example, a pulse widthmodulation (Pulse Width Modulation: PWM) circuit or the like, whichsupplies a signal for controlling a width (on time) of voltage switch-onof each of the power MOSQH1 and MOSQL1. The output (terminal for controlsignal) of the control circuit 2 is electrically connected to the inputof the driver circuit 3. The output of the driver circuit (first controlcircuit) 3 is electrically connected to a gate terminal GH of the powerMOSQH1 and a gate terminal GL of the power MOSQL1. The driver circuit 3is a circuit which controls the potentials of the gate terminals GH andGL of the power MOSQH1 and MOSQL1, respectively, in response to thecontrol signals supplied from the control circuit 2 thereby to controlthe operations of the power MOSQH1 and MOSQL1. Incidentally, VDINindicates an input source for the driver circuit.

The power MOSQH1 and MOSQL1 are connected in series between a highpotential (first power supply potential) supply terminal (first powersupply terminal) ET1 of an input power supply VIN, and a referencepotential (second power supply potential) GND supply terminal (secondpower supply terminal) ET2. That is, the power MOSQH1 is provided insuch a way that its source-to-drain path is connected in series betweenthe high potential supply terminal ET1 of the input power supply VIN andan output node (output terminal) Lx. The power MOSQL1 is provided insuch a manner that its source-to-drain path is series-connected betweenthe output node Lx and the ground potential GND supply terminal ET2.Incidentally, Dp1 indicates a parasitic diode (internal diode) of thepower MOSQH1, and Dp2 indicates a parasitic diode (internal diode) ofthe power MOSQL1.

The power MOSQH1 is of a field effect transistor for a high-side switch(high potential side: first operating voltage; hereinafter called simply“high side”) and has a switch function for storing energy in the coil Lfor supplying power to the output (input of a load circuit 4) of thenon-insulated DC-DC converter 1. The power MOS•FETQH1 is formed by an nchannel vertical field effect transistor. The vertical field effecttransistor is of an element whose channel is formed in the direction ofthickness of a semiconductor chip. As compared with a horizontal fieldeffect transistor, the vertical field effect transistor is capable ofincreasing its channel width per unit area and reducing its onresistance. It is therefore possible to realize miniaturization of theelement and attain a reduction in packaging.

On the other hand, the power MOS (second field effect transistor) QL1 isof a field effect transistor for a low-side switch (low potential side:second operating voltage; hereinafter called simply “low side”) and isalso a rectifying transistor of the non-insulated DC-DC converter 1. Thepower MOSQL1 has the function of reducing the resistance of thetransistor in sync with a frequency supplied from the control circuit 2and performing rectification. The power MOSQL1 is formed by an n channelvertical power MOS in a manner similar to the power MOSQH1. The reasonwhy the vertical type is used, is that the low-side power MOSQL1 has anadvantage that since its on time (time taken while the voltage is beingapplied) is longer than that of the power MOSQH1 for the high-sideswitch and a loss produced due to its on resistance is taken larger thaneach switching loss, as shown in the timing chart of the non-insulatedDC-DC converter 1 in FIG. 2, the vertical field effect transistor whosechannel width per unit area can be increased as compared with thehorizontal field effect transistor can be used. That is, it is becausesince the on resistance can be reduced by formation of the power MOSQL1for the low-side switch by the vertical field effect transistor, voltageconversion efficiency can be enhanced even though a current that flowsthrough the non-insulated DC-DC converter 1 increases. Incidentally, inFIG. 2, Ton indicates a pulse width at the turning on of the powerMOSQH1 for the high-side switch, and T indicates a pulse cyclerespectively.

The input capacitor Cin is electrically connected in parallel with theinput power supply VIN of FIG. 1. The input capacitor Cin is a powersupply circuit which temporarily stores energy (charge) supplied fromthe input power supply VIN and supplies the stored energy to the maincircuit of the non-insulated DC-DC converter 1. Since the input powersupply VIN is directed not only to a power supply for the non-insulatedDC-DC converter 1 alone but also to a power supply for other device, itis placed in a position far away from the non-insulated DC-DC converter1. Further, since power supply efficiency is reduced when power isdirectly supplied from the input power supply VIN to the non-insulatedDC-DC converter 1, the input power supply VIN supplies power to theinput capacitor Cin placed in a position relatively near the maincircuit of the non-insulated DC-DC converter 1, and the input capacitorCin supplies the power to the main circuit of the non-insulated DC-DCconverter 1. An input power supply potential of the input power supplyVIN ranges from approximately 5 to 12V, for example. The referencepotential GND is lower than, for example, the input power supplypotential and is 0(zero)V as a ground potential, for example. Anoperating frequency (cycle used when the power MOSQH1 and MOSQL1 areturned on and off) of the non-insulated DC-DC converter 1 is 1 MHz, forinstance.

The output node Lx for supplying an output power supply potential to theoutside is provided over a wiring that connects the source of the powerMOSQH1 of the non-insulated DC-DC converter 1 and the drain of the powerMOSQL1 thereof to each other. The output node Lx is electricallyconnected to the coil L via an output wiring and electrically connectedto the load circuit 4 via an output wiring. A Schottky barrier diode(hereinafter abbreviated as “SBD”) may electrically be connected betweenthe output wiring that connects the output node Lx and the coil L andits corresponding reference potential GND supply terminal so as tobecome parallel to the power MOSQL1. The SBD is a diode whose forwardvoltage Vf is lower than that of the parasitic diode Dp2 of the powerMOSQL1. The SBD has an anode electrically connected to the referencepotential GND supply terminal ET2 and a cathode electrically connectedto its corresponding output wiring that connects the output node Lx andthe drain of the power MOSQL1. Since a voltage drop at a dead time whenthe power MOSQL1 is turned off, can be lowered by connecting the SBD inthis way, a conduction loss of the diode can be reduced. Further, adiode recovery loss can be reduced by making a reverse recovery time(trr) earlier.

The output capacitor Cout is electrically connected between the outputwiring connecting the coil L and the load circuit 4 and the referencepotential GND supply terminal. For instance, a CPU (Central ProcessingUnit) or an MPU (Micro Processing Unit) or the like of the electronicequipment can be illustrated as the load circuit 4. Iout indicates anoutput current, and Vout indicates an output voltage, respectively.

In such a circuit, the power MOSQH1 and MOSQL1 are alternately turnedoff/on while synchronization is being achieved therebetween, whereby theconversion of a power supply voltage is carried out. That is, when thepower MOSQH1 for the high-side switch is on, a current (first current)I1 flows from the terminal ET1 electrically connected to the drain D ofthe power MOSQH1 to the output node Lx through the power MOSQH1, whereaswhen the power MOSQH1 for the high-side switch is off, a current I2flows due to a back electromotive voltage of the coil L. Turning on thepower MOSQL1 for the low-side switch when the current I2 is flowing,enables a reduction in voltage drop. The current I1 is a large currentof 20 A or so, for example.

Meanwhile, in such a non-insulated DC-DC converter 1, the parasiticinductances (L1+L2+L3+L4+L5+L6) parasitic on the main circuit around theinput capacitor Cin become large with increases in current andfrequency. In particular, a leap voltage at the turning off of thehigh-side power MOSQH1 of the non-insulated DC-DC converter 1 increases.As a result, a problem arises in that switching losses increase and alarge loss occurs.

Now, according to the discussions of the present inventors, each of suchconfigurations as shown in FIGS. 3 through 7 is illustrated as oneexample of a package configuration for reducing the parasiticinductances. FIG. 3 shows a plan view showing the interior of a package,and FIG. 4 shows a sectional view taken along line Y1-Y1 of FIG. 3,respectively. In FIGS. 3 and 4, a semiconductor chip 5 a in which ahigh-side power MOSQH1 is formed, and a semiconductor chip 5 b in whicha low-side power MOSQL1 is formed, are accommodated in the sameencapsulator (resin encapsulator) 6. The semiconductor chips 5 a and 5 bare respectively mounted over discrete die pads 7 a 1 and 7 a 2. Thesource of the high-side power MOSQH1 is electrically connected to itscorresponding die pad 7 a 2 with the power MOSQL1 mounted thereon viabonding wires (hereinafter called simply “wires”) W.

FIG. 5 shows a plan view showing the interior of a package, and FIG. 6shows a sectional view taken along line Y2-Y2 of FIG. 5, respectively.In FIGS. 5 and 6, a semiconductor chip 5 c formed with the drivercircuit 3 is also stored in the same encapsulator 6 in addition to thesemiconductor chips 5 a and 5 b. The semiconductor chip 5 c is mountedover its corresponding die pad 7 a 3 different from the die pads 7 a 1and 7 a 2. Even in the present example, semiconductor chips 5 a and 5 bare mounted over their corresponding discrete die pads 7 a 1 and 7 a 2.The source of a high-side power MOSQH1 is electrically connected to thedie pad 7 a 2 with a low-side power MOSQL1 mounted thereon via wires W.

Further, FIG. 7 shows the package configuration disclosed in the patentdocument 2. In addition to the semiconductor chips 5 a, 5 b and 5 c, aninput capacitor Cin is also accommodated within the same encapsulator 6.In this case, the source of the high-side power MOSQH1 is electricallyconnected to wirings of a wiring board 50 through wires W. The wiringsthereof are electrically connected to the drain of the low-side powerMOSQL1. The source of the low-side power MOSQL1 is electricallyconnected to its corresponding output wiring of the wiring board 50 viathe corresponding wire W.

Since the input capacitors Cin are externally provided in suchconfigurations as shown in FIGS. 3 and 4 and FIGS. 5 and 6, theparasitic inductances L1 and L6 cannot be reduced. Since the source ofthe high-side power MOSQH1 and the die pad 7 a 2 are electricallyconnected to each other by the wires W, and the source of the low-sidepower MOSQL1 and its corresponding reference potential GND areelectrically connected by the wires W, there is a limit to reduction inthe parasitic inductances L3 and L5.

Even in the configuration in which the semiconductor chips 5 a, 5 b and5 c and the input capacitor Cin are accommodated within the sameencapsulator 6 as shown in FIG. 7, they are connected by the wires W.Hence, the parasitic inductances L3 and L5 cannot be reduced and acertain degree of distance occurs between the input capacitor Cin andeach of the power MOSQH1 and MOSQL1. Therefore, there is a limit even toreductions in the parasitic inductances L1 and L6.

Thus, in the present embodiment, the high-side power MOS and thelow-side power MOS are mounted over a common die pad (tub/chip mountingsection) to reduce the parasitic inductances L3 and L4 of the parasiticinductances L1 through L6. Therefore, in the present embodiment, thehigh-side power MOS of the non-insulated DC-DC converter 1 is formed bya p channel vertical power MOS or an n channel horizontal power MOS.

A description will first be made of a configuration wherein a high-sidepower MOS is formed of a p channel vertical power MOS. FIG. 8 shows oneexample of a circuit diagram of the non-insulated DC-DC converter 1according to the first embodiment. The high-side power MOS isconstituted of a p channel vertical power MOSQH2. The function per se ofthe power MOSQH2 is identical to the power MOSQH1. The source S anddrain D of the high-side power MOSQH2 shown in FIG. 8 are placed inopposing relationship to the source S and drain D of the high-side powerMOSQH1 shown in FIG. 1. That is, the source S of the high-side powerMOSQH2 is connected to its corresponding input power supply VIN, and thedrain D of the high-side power MOSQH2 is connected to its correspondingdrain D of a low-side power MOSQL1. This is because when the high-sidepower MOS and the low-side power MOS are built in the non-insulatedDC-DC converter, they are also connected in such a manner that theirparasitic diodes Dp1 and Dp2 are connected in the opposite direction.This is also because since the p channel vertical power MOS is oppositein pn junction to an n channel vertical power MOS, the direction of theparasitic diode Dp1 of the p channel vertical power MOS also becomesopposite to the direction of the parasitic diode Dp2 of the n channelvertical power MOS. The low-side power MOSQL1 is constituted of an nchannel horizontal power MOS. Therefore, the channel characteristics ofthe high-side power MOSQH2 and the low-side power MOSQL1 are symmetricalwith each other. Configurations other than these are identical to thosedescribed in FIGS. 1 and 2 or the like.

Since the high-side power MOS is formed of the p channel vertical powerMOS in this way, the drain can be shared between the high-side powerMOSQH2 and the low-side power MOSQL1. Therefore, there is no need todistribute or separate die pads between the high-side power MOSQH1 andthe low-side power MOSQL1 as in a package configuration to be describedlater. Hence the common die pad can be utilized. It is thereforepossible to considerably reduce the parasitic inductances L3 and L4.Further, the parasitic resistance can significantly be reduced ascompared with the case in which the high-side power MOSQH1 and thelow-side power MOSQL1 are connected by wires WA. Thus, each switchingloss of the non-insulated DC-DC converter 1 can greatly be reduced.Further, since the high-side power MOSQH2 and the low-side power MOSQL1can be placed at closer distance therebetween as compared with theseparation of the high-side die pad and the low-side die pad, areduction in package size can also be realized.

The p channel vertical power MOS is generally larger than the n channelvertical power MOS in on resistance. This is because the mobility ofeach of holes corresponding to carriers of the p channel MOS is smallerthan that of each of electrons corresponding to carriers of the nchannel MOS. In the high side of the non-insulated DC-DC converter,however, each switching loss is larger than the conduction loss causedby the on resistance. The more the operating frequency of thenon-insulated DC-DC converter 1 increases in particular, the more theswitching losses are suffered. Therefore, the lowering effect of theswitching losses reducible by reducing the parasitic inductances L1through L6 is larger than the conduction loss produced due to theincrease in on resistance, and hence the whole loss can be reduced.Since, however, the p channel vertical power MOS can be reduced in onresistance and reduced in chip size too as compared with a horizontalpower MOS to be described later, a reduction in cost is enabled ascompared with the case in which the horizontal power MOS is used. Sincethe chip size of the vertical power MOS can be reduced as compared withthe horizontal power MOS, the area (size) of its die pad can also bescaled down. That is, a package size can be reduced as compared with thecase in which the horizontal power MOS is mounted over the common diepad.

Next, FIGS. 9 and 10 show one example of a package structure where a pchannel vertical power MOSQH2 is used as the high-side power MOS of thenon-insulated DC-DC converter 1. FIG. 9 shows a plan view showing theinterior of a package 10A, and FIG. 10 shows a sectional view takenalong line Y3-Y3 of FIG. 9, respectively. Incidentally, FIG. 9 is shownas seen through the interior of the package 10A to make it easy to seethe drawing. Symbol X indicates a first direction, and symbol Yindicates a second direction orthogonal to the first direction.

Two discrete semiconductor chips 5 a 2 and 5 b are accommodated withinthe package 10A in a state of being mounted onto a common die pad(tub/first chip mounting section) 7 a 4. A high-side p channel verticalpower MOSQH2 of the non-insulated DC-DC converter 1 is formed in thesemiconductor chip (first semiconductor chip) 5 a 2. A low-side nchannel vertical power MOSQL1 of the non-insulated DC-DC converter 1 isformed in the semiconductor chip 5 b.

Accommodating the semiconductor chip 5 a 2 formed with the high-sidepower MOSQH2 and the semiconductor chip 5 b formed with the low-sidepower MOSQL1 in one package 10A in this way makes it possible to reduceparasitic inductance parasitic on each wiring that connects thehigh-side power MOSQH2 and the low-side power MOSQL1. It is thereforepossible to reduce the whole loss of the non-insulated DC-DC converter1. In the first embodiment in particular, the drain of the high-side pchannel vertical power MOSQH2 and the drain of the low-side n channelvertical power MOSQL1 are electrically connected to each other through acommon die pad 7 a 4. Thus, the parasitic inductances L3 and L4 can bereduced drastically. The parasitic resistance can greatly be reduced ascompared with the case in which the high-side power MOSQH2 and thelow-side power MOSQL1 are connected by the wires WA. Since thesemiconductor chips 5 a 2 and 5 b can be placed closer to each other,the package 10A can also be reduced in size.

The semiconductor chip 5 a 2 has a square flat surface that intersectsits thickness. The semiconductor chip 5 a 2 is mounted over the die pad7 a 4 in a state in which its main surface is turned up and the backsurface thereof opposite to the main surface of the semiconductor chip 5a 2 is directed to the die pad 7 a 4. A bonding pad (hereinafter calledsimply “pad”) HSP for a source electrode of the power MOSQH2, and a padHGP for a gate electrode thereof are disposed over the main surface ofthe semiconductor chip 5 a 2. The pad HSP for the source electrode iselectrically connected to a lead (external terminal for the supply ofinput power and first external terminal) 7 b 1 through a plurality ofwires W. The lead 7 b 1 is an external terminal electrically connectedto the terminal ET1 and is placed in the neighborhood of one long sideof the die pad 7 a 4 in a state of being separated from the die pad 7 a4. The semiconductor chip 5 a 2 per se is disposed closer to the lead 7b 1 than the center of the die pad 7 a 4 as viewed in the seconddirection Y. With the layout of such a semiconductor chip 5 a 2, theparasitic inductance L2 can be reduced. This is because the length ofeach wire W for electrically connecting to the lead 7 b 1 can be madeshort as compared with the case in which the semiconductor chip 5 a 2 isplaced in the vicinity (on the lead 7 b 3 side as viewed from thecenter) of the center of the die pad 7 a 4 as viewed in the seconddirection Y. The pad HSP for the gate electrode is electricallyconnected to a lead 7 bg 1 through a wire W. The lead 7 bg 1 is anexternal terminal corresponding to the gate terminal GH to which anoutput signal from the driver circuit 3 is inputted. The lead 7 bg 1 isplaced substantially in the vicinity of the center of one long side ofthe die pad 7 a 4 in a state of being separated from the die pad 7 a 4.Further, the back surface of the semiconductor chip 5 a 2 serves as thedrain electrode of the power MOSQH2 and is electrically connected to thedie pad 7 a 4.

On the other hand, the semiconductor chip 5 b larger than thesemiconductor chip 5 a 2 in plain area is mounted over the die pad 7 a 4in a state in which its main surface is turned up and its back surfaceopposite to the main surface of the semiconductor chip 5 b is directedto the die pad 7 a 4. The semiconductor chip 5 b has a square flatsurface that intersects its thickness. A pad LSP for a source electrodeof the power MOSQL1, and a pad LGP for a gate electrode thereof aredisposed in the main surface of the semiconductor chip 5 b. The pad LSPfor the source electrode is electrically connected to a lead (externalterminal for the supply of the reference potential and second externalterminal) 7 b 2 through a plurality of wires W. The lead 7 b 2 is anexternal terminal electrically connected to the terminal ET2 and isplaced in the neighborhood of one long side of the die pad 7 a 4 in astate of being separated from the die pad 7 a 4. The positions forconnection of the plurality of wires W to the pad LSP are placed closerto the lead 7 b 2 than the center of the semiconductor chip 5 b asviewed in the second direction Y. The semiconductor chip 5 b per se isalso disposed closer to the lead 7 b 2 than the center of the die pad 7a 4 as viewed in the second direction Y. With the layout of such wires Wand semiconductor chip 5 b, the parasitic inductance L5 can be reduced.This is also identical to the reason described in the semiconductor chip5 a 2. That is, it is because the length of each wire W forelectronically connecting to the lead 7 b 2 can be made short ascompared with the case in which the semiconductor chip 5 b is placed inthe vicinity (on the lead 7 b 3 side as viewed from the center) of thecenter of the die pad 7 a 4 as viewed in the second direction Y. The padLGP is electrically connected to a lead 7 bg 2 through a wire W. Thelead 7 bg 2 is an external terminal corresponding to the gate terminalGL to which an output signal from the driver circuit 3 is inputted. Thelead 7 bg 2 is placed substantially in the vicinity of the center of onelong side of the die pad 7 a 4 in a state of being separated from thedie pad 7 a 4. Since the leads 7 bg 1 and 7 bg 2 of the semiconductorchips 5 a 2 and 5 b are disposed in the center of the die pad 7 a 4 asviewed in its longitudinal direction so as to adjoin each other, thedistances between the gate electrodes of the power MOSQH2 and MOSQL1operated in sync with each other, and the control circuit 2 can beshortened and made substantially identical in length to each other. Itis therefore possible to improve operational performance and reliabilityof the non-insulated DC-DC converter 1. Further, the back surface of thesemiconductor chip 5 b serves as the drain electrode of the power MOSQL1and is electrically connected to the die pad 7 a 4. At the other longside of the die pad 7 a 4, a plurality of leads (output externalterminals) 7 b 3 are formed integrally with the die pad 7 a 4. Theplurality of leads 7 b 3 are external terminals electrically connectedto the output node Lx.

The semiconductor chips 5 a 2 and 5 b are disposed in such a manner thatthe pads HGP and LGP for their gate electrodes are positioned on thecenter side as viewed in the first direction X. Thus, since the lengthsof input wirings W (particularly, wires WX1 and WX2) of the high-sidepower MOSQH2 and low-side power MOSQL1 can be made equal to each other,the stability of operation of the non-insulated DC-DC converter 1 can beimproved.

If the die pad 7 a 4 is merely used in common, then the plurality ofleads are laid out in various ways. However, if the leads 7 b 1 through7 b 3, 7 bg 1 and 7 bg 2 electrically connected via the plurality ofwires W are disposed on both sides as viewed in the longitudinaldirection of the die pad 7 a 4, then predetermined intervals should beprovided adjacent to both sides as viewed in the longitudinal directionof the die pad 7 a 4. Since the plurality of leads 7 b 1 through 7 b 3,7 bg 1 and 7 bg 2 are different in electric characteristic, theintervals are provided for the purpose of their insulation.

In the present embodiment in contrast, the plurality of leads (outputexternal terminals) 7 b 3 are formed integrally with the die pad 7 a 4and disposed side by side on the same side as viewed in the longitudinaldirection of the die pad 7 a 4. In other words, since the leads 7 b 1through 7 b 3, 7 bg 1 and 7 bg 2 electrically connected via theplurality of wires W are disposed side by side only on the side oppositeto the lead 7 b 3, the predetermined intervals provided for insulation(separation) from the die pad 7 a 4 are provided only on the one side asviewed in the longitudinal direction of the die pad 7 a 4. As a result,miniaturization of the package 10A can be realized as compared with thecase in which the predetermined intervals are provided on both sides ofthe die pad 7 a 4.

Such two semiconductor chips 5 a 2 and 5 b, some of leads 7 b 1 through7 b 3, 7 bg 1 and 7 bg 2, part of the die pad 7 a 4 and wires W aresealed with an encapsulator 6. The die pad 7 a 4 and the leads 7 b 1through 7 b 3, 7 bg 1 and 7 bg 2 are formed with a metal material like,for example, 42 alloy or the like as a main material. The thickness ofeach of them is approximately 200 μm, for example. As other material forthe die pad 7 a 4 and leads 7 b 1 through 7 b 3, 7 bg 1 and 7 bg 2 maybe used, with, for example, one plated with copper or one obtained bysequentially plating nickel (Ni), palladium (Pd) and gold (Au) onto thesurface of copper from the surface. Each of the wires W is made up of ametal thin line like, for example, gold (Au) or the like. Theencapsulator 6 is constituted of, for example, an epoxy resin. Due tothe reasons for attainment of a reduction in stress or the like, forexample, a phenyl curing agent, and a biphenyl thermosetting resin addedwith silicon rubber and filler or the like may be used as a material forthe encapsulator 6. A transfer mold method suitable for mass productionis used as a method for forming the encapsulator 6. The back surface ofone die pad 7 a 4 flat and substantially rectangular, for example isexposed at the back surface of the encapsulator 6. Some of the pluralityof leads 7 b 1 through 7 b 3, 7 bg 1 and 7 bg 2 are exposed at the sideface of the encapsulator 6 and on the outer periphery of the backsurface thereof.

The semiconductor chip 5 a 2 formed with the high-side power MOSQH2 willnext be explained. FIG. 11 shows an enlarged plan view of thesemiconductor chip 5 a 2 formed with the high-side power MOSQH2, FIG. 12shows a fragmentary enlarged plan view of the semiconductor chip 5 a 2shown in FIG. 11, FIG. 13 shows a sectional view taken along line X1-X1of FIG. 12, FIG. 14 shows a sectional view taken along line Y4-Y4 ofFIG. 12, and FIG. 15 is a sectional view taken along line X2-X2 of FIG.12, respectively.

A plane shape of the semiconductor chip 5 a 2 is shaped in the form of,for example, such a rectangle that the length thereof in a firstdirection X is longer than the length thereof in a second direction Y.The semiconductor chip 5 a 2 has a main surface (device forming surface:first surface) with an elemental device formed thereon, and a backsurface (back-surface electrode forming surface: second surface) placedon the opposite side thereof.

A pad HGP for a gate electrode of the power MOSQH2, gate fingers (gateelectrode patterns) 12 a and 12 b electrically connected to the pad HGPfor the gate electrode, and pads HSPs each used for a source electrodeof the power MOSQH2 are disposed in the main surface of thesemiconductor chip 5 a 2. A back surface electrode HBE for a drainelectrode thereof, which is made up of, for example, gold (Au), isdisposed in the back surface of the semiconductor chip 5 a 2. The backsurface electrode HBE is electrically connected to the die pad 7 a 4.

The pad HGP for the gate electrode is disposed in the vicinity of oneend of the semiconductor chip 5 a 2 as viewed in the first direction Xwithin the main surface of the semiconductor chip 5 a 2. The pad HGP isformed of parts of the gate fingers 12 a and 12 b exposed from anaperture or opening 13 a defined in part of a surface protective film PRcorresponding to the top layer of the semiconductor chip 5 a 2. Thesurface protective film PR is formed of, for example, a laminated filmof a silicon oxide film and a silicon nitride (Si₃N₄) film, or oneformed by laminating an organic film like a polyimide film (PiQ) overthe laminated film. One gate finger 12 a is formed near the outerperiphery of the main surface of the semiconductor chip 5 a 2 along theouter periphery thereof. The other gate finger 12 b is formed in thecenter as viewed in the second direction Y, of the semiconductor chip 5a 2 in a state of extending along the first direction X. One end of thegate finger 12 b is connected to the gate finger 12 a, whereas the otherend thereof is terminated at a position away from the gate finger 12 a.The gate fingers 12 a and 12 b are respectively brought to aconfiguration wherein, for example, a barrier metal layer like titaniumtungsten (TiW) or the like and a metal layer like aluminum (Al) or thelike are stacked on each other in order from a lower layer. The gatefingers 12 a and 12 b are formed integrally with each other. Since thegate resistance of the power MOSQH2 can be reduced owing to theprovision of such gate fingers 12 a and 12 b, such a configuration canadapt to increases in the current and frequency of the non-insulatedDC-DC converter 1. Each of the pads HSPs for the source electrode isplaced in a position where it is surrounded by the gate fingers 12 a and12 b. The pad HSP is formed of part of a conductor pattern exposed froman aperture or opening 13 b defined in part of the surface protectivefilm PR. The upper and lower pads HSPs are electrically connected toeach other at an interrupted or terminated spot of the gate finger 12 b.While each pad HSP is made up of the same metal as the gate fingers 12 aand 12 b, the pads HSP and the gate fingers 12 a and 12 b areelectrically connected to one another.

A semiconductor substrate (first semiconductor layer) 5HS thatconstitutes the semiconductor chip 5 a 2 is constituted of, for example,a p⁺ type silicon monocrystal. An epitaxial layer (second semiconductorlayer) 5HEP constituted of a p⁻ type silicon monocrystal is formed at alayer above the semiconductor substrate. A field insulating film FLDmade up of, for example, silicon oxide (SiO₂ or the like) is formed in amain surface of the epitaxial layer 5HEP. A plurality of unit transistorcells constituting the power MOSQH2 are formed in an active regionsurrounded by the field insulating film FLD and an n-type well regionNWL1 placed in a layer below the field insulating film. The power MOS isformed by connecting the plurality of unit transistor cells in parallel.

Each of the unit transistor cells is configured as, for example, a pchannel vertical power MOSQH2 of a trench gate structure. With theprovision of such a trench gate structure, miniaturization and highintegration of the unit transistor cell of the power MOSQH2 can beattained. Each unit transistor cell has a semiconductor substrate 5HSand an epitaxial layer 5HEP each having a function serving as a drainregion, n type semiconductor regions 14 n each having a function servingas a channel forming region, the p⁺ type semiconductor regions 15 p eachhaving a function serving as a source region, a trench 16 defined or dugin the direction of thickness of the epitaxial layer 5HEP, a gateinsulting film 17 formed in the bottom and side faces of each trench 16,and a gate electrode 18HG1 embedded in the trench 16 through the gateinsulating film 17 interposed therebetween.

The pad HGP for the gate electrode and the gate fingers 12 a and 12 bare electrically connected to a gate wiring 18L drawn or led out ontothe field insulating film FLD through a contact hole 20 a defined in aninsulating layer 19 a. The gate wiring 18L is made up of, for example,polycrystalline silicon low in resistance and is electrically connectedto the gate electrodes 18HG1 formed integrally with the same. Thepresent embodiment illustrates by way of example, a case in which asindicated by hatching with a satin finished surface shown in FIG. 12,the gate electrodes 18HG1 (trenches 16) are laid out in stripe form.That is, a plurality of plane band-like gate electrodes 18HG1 extendingin the second direction Y are disposed side by side in plural form alongthe first direction X within a region or area for forming each unittransistor group of the power MOSQH2. However, the plane layout shapesof the gate electrodes 18HG1 (trenches 16) are not limited to the stripeform and may be changed in various ways. The plane layout shapes may beset in plane lattice form, for example. The depth of each trench 16 isset to such an extent that it extends through the n type semiconductorregion 14 n. Incidentally, the insulating layer 19 a is formed of, forexample, PSG (Phospho Silicate Glass) or the like and providesinsulation between the gate electrodes 18HG1 and the gate wiring 18L andsource electrode pads HSPs. On the other hand, the pads HSPs areelectrically connected to the p⁺ type semiconductor regions 15 p for thesource through contact holes 20 b defined in the insulating layer 19 a.In addition, the pads HSPs are electrically connected to n⁺ typesemiconductor regions 22 n through trenches 21 dug in the n typesemiconductor regions 14 n in the epitaxial layer 5HEP and electricallyconnected to the n type semiconductor regions 14 n for channel formationthrough the n⁺ type semiconductor regions 22 n. When the n⁺ typesemiconductor regions 22 n are not formed, a large current suddenlyflows into a channel region when the current changes from off to on, sothat each transistor breaks down. Thus, as in the present embodiment,the n⁺ type semiconductor regions 22 n are formed and a load current iscaused to flow therethrough until the current is switched to on, wherebydamage of the transistor is prevented. Channels (p type channels) ofsuch a power MOSQH2 are respectively formed between the epitaxial layer5HEP and the p⁺ type semiconductor regions 15 p along the direction(direction of depth of each trench 16: direction intersecting the mainand back surfaces of the semiconductor substrate) of thickness of thesemiconductor substrate 5HS within the n type semiconductor regions 14 nopposite to the side faces of the gate electrodes 18HG1 of theindividual unit transistors through the gate insulating film 17interposed between. A drive current also flows along each channel.Incidentally, while FIG. 11 is a plan view, the gate fingers 12 a and 12b and pads HSPs are given hatching with the satin finished surface tomake it easy to see the drawing. While FIG. 12 is a plan view, the gateelectrodes 18HG1 and gate wiring 18L are given hatching with the satinfinished surface to make it easy to see the drawing. In order to make iteasy to understand the configuration, FIG. 12 is shown as seen throughthe gate electrodes 18HG1 and gate wiring 18L.

A description will next be made of the semiconductor chip 5 b formedwith the low-side power MOSQL1. FIG. 16 shows a sectional view of eachunit transistor cell of the n channel vertical power MOSQL1 of thesemiconductor chip 5 b shown in FIG. 9.

The semiconductor chip 5 b is substantially identical in basicconfiguration to the semiconductor chip 5 a 2. A plane form of thesemiconductor chip 5 b is shaped in the form of, for example, such arectangle that the length thereof in the first direction X is longerthan that thereof in the second direction Y. The semiconductor chip 5 bhas a main surface (device forming surface: first surface) with anelemental device formed thereon, and a back surface (back-surfaceelectrode forming surface: second surface) placed on the opposite sidethereof.

A pad LGP for a gate electrode of the power MOSQL1, gate fingers 12 aand 12 b electrically connected to the pad LGP for the gate electrode,and pads LSPs each used for a source electrode of the power MOSQL1 aredisposed in the main surface of the semiconductor chip 5 b. A backsurface electrode LBE for a drain electrode thereof, which is made upof, for example, gold (Au), is disposed in the back surface of thesemiconductor chip 5 b. The back surface electrode LBE is electricallyconnected to the die pad 7 a 4.

According to the discussions of the present inventors, the gateresistance of the power MOSQL1 cannot be reduced and its switching speedbecomes slow in such a structure that the gate fingers are provided onlyon the outer periphery of the main surface of the semiconductor chip 5 bin the semiconductor chip 5 b of the low-side power MOSQL1. The presentinventors have first found out the presence of a problem that when thegate resistance reaches a certain value or more in the low-side powerMOSQL1 of the non-insulated DC-DC converter 1, a self turn-on phenomenoncomes to the fore suddenly, so that a loss increases significantly. Theself turn-on phenomenon is a malfunction that when the low-side powerMOSQL1 is turned off and the high-side power MOSQH2 is turned on, thepotential of each wiring that connects the low-side power MOSQL1 and thehigh-side power MOSQH2 rises, and the gate voltage of the low-side powerMOSQL1 rises depending on the ratio between a drain-to-gate capacitanceof the low-side power MOSQL1 and a source-to-gate capacitance thereof,so that the low-side power MOSQL1 is turned on without intention. Sincethe current value of the non-insulated DC-DC converter 1 is small andits frequency is also low in the existing circumstances, the influenceof an increase in loss due to the self turn-on phenomenon is small andthe gate resistance of the low-side power MOSQL1 is not so emphasized ascompared with the gate resistance of the power MOSQH2. However, aproblem arises in that the loss due to the self turn-on phenomenonincreases with the increases in the current and frequency of thenon-insulated DC-DC converter 1 as described above. Therefore, in thefirst embodiment, the plurality of gate fingers 12 b are disposed overthe unit transistor groups in the main surface of the semiconductor chip5 b as shown in FIG. 9. Thus, since the gate resistance of the low-sidepower MOSQL1 can be reduced, the self turn-on phenomenon can besuppressed. It is therefore possible to reduce the loss of thenon-insulated DC-DC converter 1. The present embodiment can adapt evento the increases in the current and frequency of the non-insulated DC-DCconverter 1. Each of the pads LSPs for the source electrode is shaped ina flat comb-teeth form. While the gate fingers 12 a and 12 b and padsLSP and LGP are formed by patterning the same metal by means of etching,they are insulated from one another.

A semiconductor substrate (first semiconductor layer) 5LS thatconstitutes the semiconductor chip 5 b is made up of, for example, an n⁺type silicon monocrystal. An epitaxial layer (second semiconductorlayer) 5LEP formed of an n⁻ type silicon monocrystal is formed at alayer thereabove. A plurality of unit transistor cells of the powerMOSQL1 are formed in an active region surrounded by a field insulatingfilm FLD of the main surface of the epitaxial layer 5LEP and a p wellformed in a layer therebelow.

Each of the unit transistor cells is configured as, for example, an nchannel vertical power MOSQL1 of a trench gate structure. With theprovision of such a trench gate structure, miniaturization and highintegration of the unit transistor cell of the power MOSQL1 can beattained. Each unit transistor cell has a semiconductor substrate 5LSand an epitaxial layer 5LEP each having a function serving as a drainregion, p type semiconductor regions 14 p each having a function servingas a channel forming region, the n⁺ type semiconductor regions 15 n eachhaving a function serving as a source region, a trench 16 defined or dugin the direction of thickness of the epitaxial layer 5LEP, a gateinsulting film 17 formed in the bottom and side faces of each trench 16,and a gate electrode 18LG embedded in the trench 16 through the gateinsulating film 17 interposed therebetween.

The plane layout of the gate electrodes 18LG and the configuration ofconnections among the gate electrodes 18LG, gate fingers 12 a and 12 band pad LGP are identical to the semiconductor chip 5 a 2. The depth ofeach trench 16 is set to such an extent that it extends through the ptype semiconductor region 14 p. On the other hand, the pads LSPs for thesource electrode are electrically connected to the n⁺ type semiconductorregions 15 n for the source through contact holes 20 b defined in theinsulating layer 19 a. In addition, the pads LSPs are electricallyconnected to p⁺ type semiconductor regions 22 p through trenches 21 dugin the epitaxial layer 5LEP and electrically connected to the p typesemiconductor regions 14 p for channel formation through the p⁺ typesemiconductor regions 22 p. In each unit transistor cell, an operatingcurrent of such a power MOSQL1 flows between the epitaxial layer 5LEPfor the drain and the n⁺ type semiconductor regions 15 n for the sourcein the direction of thickness of the semiconductor substrate 5LS alongthe side face (i.e., the side face of each trench 16) of the gateelectrode 18LG.

Second Preferred Embodiment

A second embodiment will explain a case in which an n channel horizontalpower MOS is used for a high-side power MOS of a non-insulated DC-DCconverter. While the present embodiment is identical to FIG. 1 incircuit diagram, each p⁺ type punch-out layer is used in the n channelhorizontal power MOS. Thus, such a configuration that a drain electrodeis disposed in a main surface of a semiconductor chip and a sourceelectrode is disposed in a back surface of the semiconductor chip, istaken. Therefore, a die pad can be shared between a high-side power MOSand a low-side power MOS in a similar to the use of the p channelvertical power MOS as in the first embodiment. It is thus possible toreduce the parasitic inductances L3 and L4. The parasitic resistance ofeach wiring that electrically connects the source of the high-side powerMOS and the drain of the low-side power MOS can also be reduced. In thehigh-side power MOS, switching losses (turn-on loss and turn-off loss)look large with an increase in the operating frequency of thenon-insulated DC-DC converter 1 due to the parasitic capacitance addedto the high-side power MOS. Since, however, a gate-to-drain feedbackcapacitance can be reduced as compared with the vertical power MOS whenthe horizontal power MOS is used as the high-side power MOS, theswitching losses can be reduced. Since the parasitic inductances L3 andL4 can be reduced in a manner similar to the case in which the p channelvertical power MOS is used, the switching losses can further be reduced.

The layout of semiconductor chips 5 a 2 and 5 b in a package 10A is alsosimilar to that described in FIGS. 9 and 10. Although a plan view of thesemiconductor chip 5 a 2 is also substantially identical to FIG. 11,each pad HSP for the source electrode shown in FIG. 11 results in a padfor a drain electrode and the back surface electrode at the back surfaceof the semiconductor chip 5 a 2 results in a source electrode in thesecond embodiment. Even in the case of the second embodiment, thesemiconductor chips 5 a 2 and 5 b have gate fingers 12 a and 12 b in amanner similar to the first embodiment. Plane layouts of a gateelectrode and each gate wiring of the high-side power MOS in thesemiconductor chip 5 a 2 of the second embodiment are also identical tothose described in FIGS. 11 and 12 or the like.

FIG. 17 shows one example of a sectional view of a unit transistor cellof the semiconductor chip 5 a 2 according to the second embodiment.

p type well regions PWL1 are formed in an epitaxial layer 5HEP by, forexample, ion-implanting an impurity such as boron (B). The high-side nchannel horizontal power MOSQH3 is formed in a main surface (i.e., amain surface of the epitaxial layer 5HEP) of a semiconductor substrate5HS. The function per se of the power MOSQH3 is identical to the powerMOSQH1. A gate insulating film 17 for the power MOSQH3 is made up of,for example, a thin silicon oxide film (SiO₂ or the like) or the likeand is formed over the main surface (i.e., the main surface of theepitaxial layer 5HEP) of the semiconductor substrate 5HS by, forexample, a thermal oxidation method or the like. Gate electrodes 18HG2for the power MOSQH3 are formed over the gate insulating film 17. Thegate electrodes 18HG2 are formed by, for example, patterning apolycrystalline silicon film and a metal silicide layer (e.g., titaniumsilicide layer or cobalt silicide layer) formed over the main surface ofthe semiconductor substrate 5HS by use of a photolithography method andan etching method. n⁺ type semiconductor regions (n⁺ type diffusionlayers) 26 a each used as a source region of the power MOSQH3 are formedin the p type well regions PWL1 in such a state as to extend to one endsof the gate electrodes 18HG2. A drain region of the power MOSQH3 isformed between the adjacent gate electrodes 18HG2 and 18HG2 so as to beshared therebetween and includes an n⁻ type semiconductor region (n⁻type diffusion layer) 26 b 1 and an n⁺ type semiconductor layer (n⁺ typediffusion layer) 26 b 2. The n⁻ type semiconductor region (n⁻ typediffusion layer) 26 b 1 is formed so as to extend to the ends of therespective gate electrodes 18HG2. The n⁺ type semiconductor region (n⁺type diffusion region) 26 b 2 is provided away by the n⁻ typesemiconductor region 26 b 1 from each of the gate electrodes 18HG2 andset higher than the n⁻ type semiconductor region 26 b 1 in impurityconcentration. That is, the drain region is configured as an LDD(Lightly Doped Drain) structure. The n⁻ type semiconductor region 26 b 1and the n⁺ type semiconductor region 26 b 2 are respectively formed by,for example, ion-implanting an impurity such as phosphorous (P).Channels (n type channels) of such a power MOSQH3 are located above thep type well regions PWL1 opposite to the lower surfaces of the gateelectrodes 18HG2 through the gate insulating film 17 interposedtherebetween and are formed between the n⁺ type semiconductor regions(n⁺ type diffusion layers) 16 a and the n⁻ type semiconductor region (n⁻type diffusion layer) 26 b 1 and n⁺ type semiconductor region (n⁺ typediffusion layer) 26 b 2 along the main surface of the semiconductorsubstrate 5HS. Incidentally, p⁺ type semiconductor regions 27 a (the p⁺type punch-out layers) 27 a are formed in the epitaxial layer 5HEP. Thep⁺ type semiconductor region 27 a is formed by, for instance,ion-implanting the impurity such as boron (B) and formed in such animpurity distribution as to reach the semiconductor substrate 5HS fromthe main surface of the epitaxial layer 5HEP.

An insulating layer 19 b constituted of, for example, a silicon oxidefilm or the like is formed over the main surface of the semiconductorsubstrate 5HS so as to cover the gate electrodes 18HG2. Source wirings28SL and a drain wiring 28DL are formed over the insulating layer 19 b.The source wiring 28SL and the drain wiring 28DL are respectivelyconstituted of a laminated film obtained by depositing an aluminum alloyfilm over an aluminum alloy or a barrier film, for example. The sourcewirings 28SL are electrically connected to their corresponding the n⁺type semiconductor regions 26 a for the source and the p⁺ typesemiconductor regions 27 a for the punch-out layer through contact holes20 b defined in the insulating layer 19 b. Therefore, the n⁺ typesemiconductor regions 26 a of the high-side power MOSQH3 are connectedto their corresponding p⁺ type semiconductor regions 27 a through thesource wirings 28SL and electrically connected to the back surfaceelectrode HBE of the back surface of the semiconductor substrate 5HSthrough the semiconductor substrate 5HS. That is, the back surfaceelectrode HBE serves as the source electrode of the high-side powerMOSQH3, and the reference potential GND is applied thereto. The drainwiring 28DL is electrically connected to its corresponding n⁺ typesemiconductor region 26 b 2 through a contact hole 20 c defined in theinsulating layer 19 b.

An insulating layer 19 c is deposited over the insulting layer 19 b soas to cover the source wirings 28SL and the drain wiring 28DL. Theinsulating layer 19 c is constituted of the same insulating material asthe insulating layer 19 b. A pad HDP for the drain electrode and a padHGP for each gate electrode are disposed in an upper surface (the mainsurface of the semiconductor chip 5 a 2) of the insulating layer 19 c.Configurations of the pads HDP and HGP are identical to the pad HGPemployed in the first embodiment. The pad HDP is electrically connectedto the drain wiring 28DL via a through hole 29 a defined in theinsulating layer 19 c. The pad HDP is electrically connected to itscorresponding lead 7 b 1 through the wires WA1 (see FIG. 9). The pad HGPis electrically connected to the gate electrodes 18HG2 through wiringsformed in the semiconductor chip 5 a 2. Incidentally, a surfaceprotective film PR is formed at the top layer of the main surface of thesemiconductor chip 5 a 2 in a manner similar to the first embodimenteven in this case. Part thereof is made open to expose the pads HGP andHDP.

Third Preferred Embodiment

A third embodiment will explain a configuration wherein threesemiconductor chips constituting a non-insulated DC-DC converter areaccommodated within one package.

FIG. 18 shows an overall plan view illustrating a main surface side of apackage 10B employed in the third embodiment, FIG. 19 shows a side viewof the package 10B shown in FIG. 18, and FIG. 20 shows an overall planview illustrating a back surface side of the package 10B shown in FIG.18, respectively.

The package 10B of the third embodiment is provided as a QFN (Quad FlatNon-leaded package) configuration, for example. However, the package 10Bis not limited to the QFN configuration and can be changed in variousways. The package 10B may be formed as a flat package configurationlike, for example, a QFP (Quad Flat Package), an SOP (Small Out-linePackage) or the like.

An encapsulator 6 that constitutes the package 10B has an outwardappearance shaped in the form of a thin plate. Back surfaces of two diepads (first and second chip mounting sections) 7 a 3 and 7 a 5 flat andsubstantially rectangular, for example are exposed from a back surfaceof the encapsulator 6. A material for each of the die pads 7 a 3 and 7 a5 is identical to the die pads 7 a 1, 7 a 2 and 7 a 4 referred to above.Some of a plurality of leads (external terminals) 7 b are exposed alongthe outer periphery of the encapsulator 6 from the four side faces ofthe encapsulator 6 and the outer periphery of the back surface thereof.As will be described later, the semiconductor chips 5 a 2 and 5 b arerespectively mounted over a main surface of the die pad 7 a 5. Thesemiconductor chip 5 c is mounted over a main surface of the die pad 7 a3. A positioning taper TR1 (index mark) is formed at one corner of thedie pad 7 a 3. Incidentally, in the present structure, both the backsurfaces (surfaces opposite to the surfaces over which the semiconductorchips 5 a 2, 5 b and 5 c are mounted) of the die pads 7 a 3 and 7 a 5and the back surfaces (junction surfaces joined or bonded to terminalsof a wiring board) of the leads 7 b exist in a mounting surface (surfaceopposite to the wiring board when the package 10B is mounted onto thewiring board) of the package 10B.

Next, FIG. 21 shows an overall plan view showing a main surface side ofthe package 10B as seen through the interior of the package 10B shown inFIG. 18, FIG. 22 shows a sectional view taken along line Y5-Y5 of FIG.21, FIG. 23 shows a sectional view taken along line X3-X3 of FIG. 21,and FIG. 24 shows an overall plan view of the semiconductor chip 5 b inthe package 10B, respectively.

Some of the two die pads 7 a 3 and 7 a 5, the semiconductor chips 5 a 2and 5 b mounted over the die pad 7 a 5, the semiconductor chip 5 cmounted over the die pad 7 a 3, wires WA1, WA2 and WB, and some of theleads 7 are encapsulated in the package 10B.

The die pads 7 a 3 and 7 a 5 are disposed adjacent to each other in astate of being separated from each other with a predetermined intervalprovided therebetween. Heat generated upon the operations of thesemiconductor chips 5 a 2, 5 b and 5 c are mainly radiated from the backsurface sides of the die pads 7 a 3 and 7 a 5 to the outside through thedie pads 7 a 3 and 7 a 5 from the back surfaces of the semiconductorchips 5 a 2, 5 b and 5 c. Therefore, the die pads 7 a 3 and 7 a 5 arerespectively formed larger than the areas of the semiconductor chips 5 a2, 5 b and 5 c. Thus, the radiation of the non-insulated DC-DC converter1 can be improved.

Parts of the outer peripheries of the back surface sides of the die pads7 a 3 and 7 a 5 and the leads 7 b are formed with half etching regionssuch that their thicknesses become thin. This is because the adhesionbetween each of the die pads 7 a 3 and 7 a 5 and leads 7 b and theencapsulator 6 is improved to reduce or prevent peeling of the die pads7 a 3 and 7 a 5 and leads 7 b and their deformations and failures.

The semiconductor chip 5 a 2 formed with the high-side power MOSQH2 andthe low-side power MOSQL1 are mounted over the largest die pad 7 a 5 ina state in which their main surfaces are being turned up. Since theparasitic inductances L3 and L4 can be reduced with the mounting of thesemiconductor chips 5 a 2 and 5 b over the same die pad 7 a 5 even inthe case of the third embodiment, switching losses can be reduced. Sincethe semiconductor chip 5 a 2 formed with the high-side power MOSQH2 andthe semiconductor chip 5 b formed with the low-side power MOSQL1 can bedisposed close to each other as compared with the case in which thehigh-side power MOS is formed of an n channel vertical power MOS, thepackage 10B can be reduced in size.

The configuration of the semiconductor chip 5 a 2 is identical to onedescribed in FIGS. 9 through 15 showing the first embodiment. Thehigh-side power MOSQH2 of the semiconductor chip 5 a 2 is constituted ofa p channel vertical power MOS. Pads HSPs for a source electrode, of thepower MOSQH2 and a pad HGP thereof for a gate electrode are disposed inthe main surface of the semiconductor chip 5 a 2. The pads HSPs for thesource electrode are electrically connected to leads 7 b 1 (7 b) througha plurality of wires WA1 and electrically connected to pads for a sourceelectrode, of a driver circuit 3 of the semiconductor chip 5 c through aplurality of wires WB. The pad HGP for the gate electrode iselectrically connected to pads for an output (drain) electrode, of thedriver circuit 3 of the semiconductor chip 5 c through a plurality ofwires WB. Further, a drain electrode of the power MOSQH2 lying in theback surface of the semiconductor chip 5 a 2 is electrically connectedto a plurality of leads 7 b 3 (7 b) formed integrally with the outerperiphery of the die pad 7 a 5 and a drain electrode of the low-sidepower MOSQL1 of the semiconductor chip 5 b through the die pad 7 a 5.The leads 7 b 3 are electrically connected to the output node Lx.Incidentally, the wires WA1 are disposed in zigzags in such a mannerthat the wires WA1 adjacent to one another in the first direction X arealternately connected to the pads HSPs placed above and below.

The semiconductor chip 5 a 2 is disposed closer to the leads 7 b 1 thanthe center of the die pad 7 a 5. Thus, since the lengths of the wiresWA1 for electrically connecting the pads HSPs for the source electrodeof the power MOSQH2 and the leads 7 b 1 can be shortened, the parasiticinductance L2 between the source of the power MOSQ1 and the terminal ET1can be reduced. The semiconductor chip 5 a 2 is disposed such that itslong side extends along the direction (first direction X) adjacent tothe leads 7 b 1. Thus, since the wires WA1 can be disposed in pluralform, the parasitic inductance L2 between the source of the power MOSQ1and the terminal ET1 can be reduced. With the formation of thesemiconductor chip 5 a 2 in rectangular form, the length of each gatewiring (gate electrode) formed of polysilicon, extending in the seconddirection Y of FIG. 21 can be shortened. It is therefore possible toreduce gate resistance of the power MOSQH2. Further, the semiconductorchip 5 a 2 is disposed in such a manner that the distance between thesemiconductor chips 5 a 2 and 5 c becomes shorter than the distancebetween the semiconductor chips 5 a 2 and 5 b, particularly, the pad HGPof the semiconductor chip 5 a 2 and the pad of the semiconductor chip 5c are close to each other in terms of the distance therebetween. Thisshows a configuration which has considered that in the high-side powerMOSQH2, an increase in the inductance of its gate greatly influences anincrease in switching loss. Since the semiconductor chip 5 a 2 can bedisposed close to the semiconductor chip 5 c, the length of each of thewires WB that electrically connect the pad HGP of the power MOSQH2 andthe output electrode pads of the driver circuit 3 can be shortened.Therefore, the inductance that is parasitic on the gate of the powerMOSQH2 can be reduced, and the switching losses of the power MOSQH2 canbe reduced. Since the parasitic inductance between the driver circuit 3and the power MOSQH2 can be reduced, the speed of transfer of eachcontrol signal can be improved. With the above-described layout ofsemiconductor chip 5 a 2, the switching losses of the power MOSQH2 canbe reduced and voltage conversion efficiency of the non-insulated DC-DCconverter 1 can be enhanced.

While the wires WA1 and WB2 are formed of gold (Au), for example, onesthicker than the wires WB are used as the wires WA1. Thus, since wiringinductance on the source side of the power MOSQH2 can be reduced, theswitching losses of the non-insulated DC-DC converter 1 can be reducedand the voltage conversion efficiency can be enhanced.

On the other hand, pads LSPs for a source electrode of the power MOSQL1and a pad LGP for a gate electrode are disposed in the main surface ofthe semiconductor chip 5 b. The pads LSPs are electrically connected toleads 7 b 2 (7 b) through a plurality of wires WA2 and electricallyconnected to the source electrode pads of the driver circuit 3 of thesemiconductor chip 5 c through a plurality of wires WB. The pad LGP forthe gate electrode is electrically connected to the pads for the output(drain) electrode of the driver circuit 3 of the semiconductor chip 5 cthrough a plurality of wires WB. Further, the drain electrode of thepower MOSQL1 at the back surface of the semiconductor chip 5 b iselectrically connected to the leads 7 b 3 (7 b) and the drain electrodeof the high-side power MOSQH2 of the semiconductor chip 5 a 2 throughthe die pad 7 a 5.

The semiconductor chip 5 b formed with the low-side power MOSQL1 isshaped in the form of a rectangle whose length in the first direction Xof FIGS. 21 and 24 is longer than the length thereof in the seconddirection Y. A pad LGP for a gate electrode, of the power MOSQL1, gatefingers 12 a and 12 b, and pads LSPs for a source electrode, of thepower MOSQL1 are disposed over the main surface of the semiconductorchip 5 b. A back surface electrode for a drain electrode, which is madeup of, for example, gold (Au), is disposed over the back surface of thesemiconductor chip 5 b.

The pad LGP for the gate electrode is disposed in the neighborhood ofthe corner at the main surface of the semiconductor chip 5 b and formedby some of the gate fingers 12 a and 12 b exposed through an opening 13c defined in part of a surface protective film corresponding to the toplayer of the semiconductor chip 5 b. One gate finger 12 a is formed nearthe outer periphery of the main surface of the semiconductor chip 5 a 2along the outer periphery thereof. The other plural gate fingers 12 bare formed in a state of extending from one long side of thesemiconductor chip 5 b to the other long side thereof. One end of eachgate finger 12 b is connected to the gate finger 12 a, whereas the otherend thereof is terminated at a position away from the gate finger 12 a.Since the gate resistance of the power MOSQL1 can be reduced owing tothe provision of such gate fingers 12 a and 12 b, such a configurationcan adapt to increases in the current and frequency of the non-insulatedDC-DC converter 1. Each of the pads LSPs for the source electrode isplaced in a position where it is surrounded by the gate fingers 12 a and12 b. The pad LSP is formed of part of a conductor pattern exposed froman aperture or opening defined in part of the surface protective filmPR. While each pad LSP is made up of the same metal as the gate fingers12 a and 12 b, the pads LSPs and the gate fingers 12 a and 12 b areelectrically insulated from one another.

While the semiconductor chip 5 b is disposed along the semiconductorchip 5 a, the semiconductor chip 5 b is separated from the semiconductorchip 5 b and disposed away from the center of the die pad 7 a 2 so as toapproach the leads 7 b 2. That is, the semiconductor chip 5 b isdisposed closer to the leads 7 b 2 connected with a terminal ET2supplied with a reference potential GND. Connecting points of wires WA2to the pads LSPs for the source electrode are disposed closer to theleads 7 b 2 than the center of the semiconductor chip 5 b. Owing tothese, the lengths of the wires WA2 for electrically connecting the padsLSPs of the power MOSQL1 and the leads 7 b 2 can be shortened. The twosides corresponding to the long and short sides intersecting each other,of the semiconductor chip 5 b are disposed along the layout shapes (Lshape as viewed in the plane) of the plural leads 7 b 2. Particularly,the pads LSPs for the source electrode of the power MOSQL1 are broughtto such shapes as to extend along the layout shapes of the plural leads7 b 2. Thus, the wires WA2 can be disposed in plural numbers. Further,the plural leads 7 b 2 are placed along the two sides perpendicular toeach other, of the die pad 7 a 5 and connected to a flat L-shaped wiringsection 7 c that extends along the two sides. By collectively connectingthe plural leads 7 b 2 to the wiring section 7 c in this way, the pluralleads 7 b 2 increase in volume as compared with their division.Therefore, wiring resistance can be reduced and the reference potentialGND can be enhanced. This configuration is such a configuration whichhas considered that an increase in on resistance on the source side, ofthe low-side power MOSQL1 greatly influences an increase in switchingloss. Since the on resistance on the source side of the power MOSQL1 canbe reduced owing to such a configuration as described above, theconduction loss of the power MOSQL1 can be lowered. Since variations inparasitic impedance produced in the wires WA2 can be reduced, variationsin the magnitude of current flowing through each wire WA2 can also bereduced. Thus, voltage conversion efficiency of the non-insulated DC-DCconverter 1 can be improved. The reference potential GND can be enhancedand hence the stability of operation of the non-insulated DC-DCconverter 1 can be improved.

The wires WA2 and WB are both made up of, for example, gold (Au),whereas the wires WA2 make use of ones thicker than the wires WB. Withthe use of the thick wires WA2 as the wires electrically connected tothe source of the power MOSQL1, wiring resistance on the source side ofthe power MOSQL1 can be reduced. Therefore, the on resistance of thepower MOSQL1 can be reduced. It is thus possible to improve voltageconversion efficiency of the non-insulated DC-DC converter 1.

Since the die pad 7 a 5 on which the semiconductor chip 5 b formed withthe low-side power MOSQL1 highest in heating value is mounted, and thedie pad 7 a 3 on which the semiconductor chip 5 c formed with the drivercircuit 3 is mounted, are separated from each other, heat generated atthe semiconductor chip 5 b can be prevented from being transferreddirectly to the die pad 7 a 3. Owing to these, the stability ofoperation of the non-insulated DC-DC converter 1 can be improved.

Further, the semiconductor chip 5 c formed with the driver circuit 3 ismounted over the die pad 7 a 3 placed on the upper right side of FIG. 21and smallest in area in a state of its main surface being turned up. Inaddition to the above pads, pads for respective signal input (gate)electrodes of the driver circuit 3, and source electrode pads are placedin the main surface of the semiconductor chip 5 c. The gate electrodepads are electrically connected to leads 7 b 4 (7 b) through a pluralityof wires WB. The source electrode pads are electrically connected toleads 7 b 5 (7 b) formed integrally with the die pad 7 a 3 through aplurality of wires.

The semiconductor chip 5 c formed with the driver circuit 3 is alsoshaped in the form of a flat rectangle. The pads connected to the powerMOSQH2 and MOSQL1 are disposed in the main surface of the semiconductorchip 5 c along two sides placed on the sides adjacent to thesemiconductor chips 5 a 2 and 5 b respectively. Thus, since the lengthof each wire WB can further be shortened, the parasitic inductanceproduced in each wiring path can further be reduced. Since thesemiconductor chip 5 a 2 needs a desire to reduce the switching lossesrather than the on resistance as described above, the distance betweenthe semiconductor chip 5 c and the semiconductor chip 5 a 2 is providedso as to be shorter than the distance between the semiconductor chip 5 cand the semiconductor chip 5 b as described above, and additionally,even as to the wires WB, the wires WB respectively electricallyconnected to the source and gate of the power MOSQH2 are formed shorterthan the wires WB respectively electrically connected to the source andgate of the power MOSQL1. Incidentally, ones thinner than the wires WA1and WA2 are used as the wires WB. This is because when the thick wiresare used, the sizes of the pads over the main surface of thesemiconductor chip 5 c should also inevitably be increased, thus causingan increase in chip size and a rise in manufacturing cost.

The semiconductor chips 5 a 2, 5 b and 5 c are different in outer size(area) due to the differences among their characteristics. The outersize of the semiconductor chip 5 a 2 is formed larger than that of thesemiconductor chip 5 c. The outer size of the semiconductor chip 5 b isformed larger than that of the semiconductor chip 5 a 2. Since thesemiconductor chip 5 c having the driver circuit 3 is a control circuitthat controls the gates of the power MOSQH2 and MOSQL1, it is desirablethat the outer size of each elemental device is set as small as possiblein consideration of the size of the whole package. On the other hand, itis desirable that the on resistance produced in each transistor isreduced as much as possible in each of the power MOSQH2 and MOSQL1.Since the reduction in on resistance can be realized by expanding achannel width per unit transistor cell area, the outer sizes of thesemiconductor chips 5 a 2 and 5 b are formed larger than the outer sizeof the semiconductor chip 5 c. Further, since the low-side power MOSQL1is longer in on time than the high-side power MOSQH2 as shown in FIG. 2,it is necessary to lower the on resistance of the power MOSQL1 than thatof the power MOSQH2. Therefore, the outer size of the semiconductor chip5 b is formed larger than that of the semiconductor chip 5 a 2.

Fourth Preferred Embodiment

A fourth embodiment will explain a configuration wherein threesemiconductor chips constituting a non-insulated DC-DC converter areaccommodated or held in one package and a high-side power MOS is formedof an n channel horizontal power MOS.

FIG. 25 shows an overall plan view illustrating a main surface side of apackage 10B of the fourth embodiment as seen through the interior of thepackage 10B, and FIG. 26 shows a sectional view of a unit transistorcell of a semiconductor chip 5 a 2 formed with a high-side power MOSQH3in the package 10B shown in FIG. 25, respectively. Incidentally, asectional view taken along line Y5-Y5 of FIG. 25 is identical to FIG.22, and a sectional view taken along line X3-X3 of FIG. 25 is identicalto FIG. 23.

The layouts of leads 7 b, wires WA1, WA2 and WB, die pads 7 a 3 and 7 a5, and semiconductor chips 5 a 2, 5 b and 5 c are identical to thosedescribed in the third embodiment. The present embodiment is differenttherefrom in that a pad HSP for a source electrode, of the high-sidepower MOSQH3 is disposed even in a main surface (corresponding to thesame surface as for the layouts of a pad HGP for a gate electrode andpads HDPs for a drain electrode) of the semiconductor chip 5 a 2 in astate of being electrically isolated from the pads HGP and HDP.

Although a device structure per se formed in the semiconductor chip 5 a2 shown in FIG. 26 is identical to one shown in FIG. 17, the pad HSP forthe source electrode is drawn out even to the main surface of thesemiconductor chip 5 a 2 by changing the configuration of a wiringlayer. That is, source wirings 28SL of the semiconductor chip 5 a 2 areelectrically connected to the pad HSP placed over the main surface ofthe semiconductor chip 5 a 2 through a through hole 29 b defined in aninsulating layer 19 c. Incidentally, a back surface electrode HBE alsoserves as the source electrode as mentioned in the second embodiment.

As shown in FIG. 25, the source electrode pad HSP placed over the mainsurface of the semiconductor chip 5 a 2 is electrically connected topads for a source electrode of a driver circuit 3 placed over itscorresponding main surface of the semiconductor chip 5 c through aplurality of wires WB. In the present embodiment, the wires WB thatconnect the pad HSP of the main surface of the semiconductor chip 5 a 2and the source electrode pads of the main surface of the semiconductorchip 5 c are disposed so as to become substantially horizontal. Thesource electrode pads of the driver circuit 3 of the semiconductor chip5 c and the die pad 7 a 5 may be electrically connected to one anotherby wires WB. Since, however, the lengths of the wires WB can beshortened by electrically connecting the source electrode pad HSP of themain surface of the semiconductor chip 5 a 2 and the source electrodepads of the main surface of the semiconductor chip 5 c through aplurality of wires WB as described above, the parasitic inductance L3can be reduced. It is therefore possible to reduce switching losses ofthe high-side power MOSQH3. Thus, voltage conversion efficiency of thenon-insulated DC-DC converter 1 can be improved.

Fifth Preferred Embodiment

A fifth embodiment will explain a configuration wherein lead plates eachmade up of a metal are used in place of the wires WA in the package 10Ashown in FIG. 9.

FIG. 27 shows an overall plan view illustrating a main surface side of apackage 10C of the fifth embodiment as seen through the interior of thepackage 10C, and FIG. 28 shows a sectional view taken along line Y6-Y6of FIG. 27, respectively. Incidentally, FIG. 27 shows lowersemiconductor chips 5 a 2 and 5 b as seen through the lead plates tomake it easy to see the drawing. A high-side power MOS corresponding toeither a p channel vertical power MOSQH2 or an n channel horizontalpower MOSQH3 is formed in the semiconductor chip 5 a 2.

In the fifth embodiment, pads (pads HSPs for a source electrode wherethe p channel vertical power MOSQH2 is formed in the semiconductor chip5 a 2, and pads HDPs for a drain electrode where the n channelhorizontal power MOSQH3 is formed in the semiconductor chip 5 a 2)placed over a main surface of the semiconductor chip 5 a 2 formed withthe high-side power MOS, and leads 7 b 1 for an input power supply VINare electrically connected to one another by a lead plate 30 a. PadsLSPs for a source electrode, which are placed over a main surface of thesemiconductor chip 5 b formed with a low-side power MOS, and leads 7 b 2for a reference potential GND are electrically connected to one anotherby a lead plate 30 b. In the present embodiment, the lead plates 30 aand 30 b are covered with an encapsulator 6 over their entirety.

The lead plates 30 a and 30 b are respectively made up of a metal highin conductivity and thermal conductivity like, for example, copper (Cu)or aluminum (Al) or the like and disposed so as to cover the majority ofthe main surfaces of the semiconductor chips 5 a 2 and 5 b that serve asheat generation sources. One end of the lead plate 30 a is bonded andelectrically connected to the pads HSPs (or pads HDPs) through ajunction layer 31. The other end of the lead plate 30 a is bonded andelectrically connected to the leads 7 b 1 through the junction layer 31.One end of the lead plate 30 b is bonded and electrically connected tothe pads LSPs through a junction layer 31. The other end of the leadplate 30 b is bonded and electrically connected to the leads 7 b 2through the junction layer 31. The junction layers 31 are made up of,for example, lead (Pb)-tin (Sn) solder or gold (Au) or the like. Aconductive resin can also be used as the junction layers 31. Pads HGPand LGP for gate electrodes and leads 7 bg 1 and 7 bg 2 are electricallyconnected by wires W respectively.

According to the fifth embodiment, the parasitic inductances L2 and L5can be reduced by use of the lead plates 30 a and 30 b. Parasiticresistance can also be reduced as compared with the wires W. It is thuspossible to further reduce switching losses and conduction losses of anon-insulated DC-DC converter 1 and to further improve voltageconversion efficiency of the non-insulated DC-DC converter 1.

Sixth Preferred Embodiment

A sixth embodiment will explain a configuration wherein lead plates areexposed onto the surface of a package.

FIG. 29 shows an overall plan view illustrating an upper surface(corresponding to a surface opposite to a mounting surface of a package10D where the package 10D is mounted to a printed wiring board) of thepackage 10D according to the sixth embodiment, and FIG. 30 shows asectional view taken along line Y6-Y6 of FIG. 29, respectively.Incidentally, an internal plan view of the package 10D is identical toFIG. 27.

In the sixth embodiment, parts of lead plates 30 c and 30 d are exposedfrom the upper surface of the package 10D. Thus, radiation can beenhanced. Allowing the lead plates 30 c and 30 d to have a radiatingfunction makes it unnecessary to add other parts for radiation.Therefore, the process of assembling a semiconductor device can besimplified as compared with the addition of the radiating parts, and thetime required to assemble the semiconductor device can be shortened.Since the number of parts can be reduced, the cost of the semiconductordevice can be cut down. Incidentally, the material for the lead plates30 c and 30 d and their plane shapes are respectively identical to thelead plates 30 a and 30 b.

Depressions (chamfered portions) 32 are formed on the upper outerperipheries of the lead plates 30 c and 30 d. Thus, a resin for anencapsulator 6 is chamfered onto the depressions 32 of the lead plates30 c and 30 d, thereby making it possible to improve the strength ofbonding between the lead plates 30 c and 30 d and the encapsulator 6. Itis therefore possible to suppress or prevent a defective condition thatthe lead plates 30 c and 30 d come off. The depressions 32 may beprovided on the lower outer peripheries (on the sides nearersemiconductor chips 5 a 2 and 5 b) of the lead plates 30 c and 30 d.Configurations other than these are identical to those in the first,second and fifth embodiments.

FIG. 31 shows a sectional view illustrating one example of aconfiguration wherein a radiating fin (heat sink) 33 is bonded onto theupper surface of the package 10D shown in FIGS. 29 and 30. The radiatingfin 33 is made up of a metal like, for example, copper (Cu) or aluminum(Al) or the like and bonded to the upper surface of the package 10D andexposed surfaces of the lead plates 30 c and 30 d through an insulativeadhesive 34 like, for example, silicon rubber or the like. A pluralityof depressions and projections are provided at an upper portion of theradiating fin 33. Bonding such a radiating fin 33 thereto enables afurther improvement in radiation.

Seventh Preferred Embodiment

A seventh embodiment will explain a configuration wherein an inputcapacitor Cin is mounted onto a package.

FIG. 32 shows an overall plan view illustrating an upper surface(corresponding to a surface opposite to a mounting surface of a package10D where the package 10D is mounted to a printed wiring board) of apackage 10D of the seventh embodiment, FIG. 33 shows an overall planview illustrating a main surface side of the package 10D as seen throughthe interior of the package shown in FIG. 32, and FIG. 34 shows asectional view taken along line Y7-Y7 of FIG. 33, respectively.

In the seventh embodiment, the input capacitor Cin is directly mountedover the upper surface of the package 10D. That is, when the inputcapacitor Cin is seen in the plane, the input capacitor Cin is disposedin such a way that some of the input capacitor Cin are superimposed onboth of the semiconductor chips 5 a 2 and 5 b. In the configuration ofthe package 10D, the lead plate 30 c is connected to an input powersupply VIN, whereas the lead plate 30 d is connected to a groundpotential GND. Therefore, the input capacitor Cin can directly bemounted over upper surfaces from which the two lead plates 30 c and 30 dare exposed, so as to act as a bridge between the lead plates 30 c and30 d in the package 10D. Since the input capacitor Cin is exposed to theoutside in the seventh embodiment, this is suitable for dissipating heatgenerated in the input capacitor Cin per se.

One of a pair of electrodes 35 a of the input capacitor Cin is bondedand electrically connected to the lead plate 30 c via a junction layer36 interposed therebetween, whereas the other thereof is bonded andelectrically connected to the lead plate 30 d via the junction layer 36interposed therebetween. With the existence of the lead plates 30 c and30 d, flatness and sufficient connecting areas can be ensured forconnecting surfaces of the pair of electrodes 35 a of the inputcapacitor Cin. Therefore, connection ease and reliability of the inputcapacitor Cin can be improved.

The junction layer 36 that bonds the input capacitor Cin onto the leadplates 30 c and 30 d, is constituted of, for example, lead (Pb)-tin (Sn)solder or gold (Au) or the like in a manner similar to a junction layer31 that bonds the lead plates 30 c and 30 d to source electrodes HSPs(or drain electrodes HDPs) and leads 7 b 1 and 7 b 2. Upon thefabrication of the package 10D, however, the input capacitor Cin ismounted after the lead plates 30 c and 30 d are bonded onto the sourceelectrodes HSPs (or drain electrode HDPs) and leads 7 b 1 and 7 b 2 bythe junction layer 31. Therefore, the melting point of the junctionlayer 36 for bonding the input capacitor Cin should be kept lower thanthat of the junction layer 31 for bonding the lead plates 30 c and 30 d.Thus, for example, a gold bump having a melting point ranging from 400°C. to 450° C., or high-temperature solder (lead-tin solder) having amelting point ranging from 350° C. to 400° C. is used for the junctionlayer 31 used for the bonding of the lead plates 30 c and 30 d. Forexample, high-temperature solder (lead-tin solder), which has a meltingpoint ranging from 350° C. to 400° C. and is lower than the meltingpoint of the junction layer 36, is used for the junction layer 36 usedfor the bonding of the input capacitor Cin.

Incidentally, FIG. 35 shows a partly broken perspective viewillustrative of one example of the input capacitor Cin. The inputcapacitor Ci includes a pair of electrodes 35 a respectively disposed atboth ends thereof, and a plurality of internal electrodes 35 b, anddielectrics 35 c interposed among the plural internal electrodes 35 b.The internal electrodes 35 b are alternately disposed in such a mannerthat ones connected to one of the pair of electrodes 35 a and onesconnected to the other thereof are opposite to one another. The pair ofelectrodes 35 a has a configuration wherein a plated layer made of, forexample, nickel and a plated layer made of, for example, tin aresequentially applied onto the surface of a bedding or base electrodemade of, for example, silver. The internal electrodes 35 b comprise, forexample, palladium (Pd), copper or nickel. The dielectrics 35 c are madeup of, for example, titanium oxide, calcium zirconate or bariumtitanate.

Thus, in the seventh embodiment, the input capacitor Cin can directly bemounted onto the upper surface of the package 10D. That is, the inputcapacitor Cin can be disposed in a near position directly above each ofthe semiconductor chips 5 a 2 and 5 b. Therefore, the parasiticinductances L1 and L6 can be reduced and the efficiency of power supplycan be improved. That is, since all the parasitic inductances L1 throughL6 can be reduced in the package 10D of the seventh embodiment,switching losses of the non-insulated DC-DC converter 1 can be reducedand an improvement in the efficiency of a system is enabled.

A user is able to select, according to the configuration of the entiresystem of the non-insulated DC-DC converter 1, a case in which theradiating fin 33 is mounted over the upper surface of the package 10D asshown in FIG. 31 illustrative of the sixth embodiment and a case inwhich the input capacitor Cin is mounted over the upper surface of thepackage 10D as described in the seventh embodiment. When it is desiredto reduce the on resistance of the system, for example, the radiatingfin 33 may preferably be mounted. On the other hand, when it is desiredto reduce the switching losses of the system, for example, the inputcapacitor Cin may preferably be mounted.

Eighth Preferred Embodiment

An eighth embodiment will explain a configuration wherein the inputcapacitor is accommodated in a package.

FIG. 36 shows a sectional view illustrative of a spot corresponding toline Y7-Y7 of FIG. 32 in a package 10E of the eighth embodiment.Incidentally, a plan view of the package 10E is identical to FIG. 27.

While the input capacitor Cin is connected to lead plates 30 a and 30 bthrough a junction layer 36 interposed therebetween in the eighthembodiment in a manner similar to the seventh embodiment, the inputcapacitor Cin is accommodated in an encapsulator 6.

The eighth embodiment is capable of obtaining the following advantageouseffects in addition to the effects obtained in the seventh embodiment.That is, the eighth embodiment can obtain the advantages that it is notnecessary for a user to mount the input capacitor Cin, and extra effortsare not taken upon packaging. Since such a configuration as not toexpose the lead plates 30 a and 30 b is taken, the fabrication of thepackage 10E is easy.

Ninth Preferred Embodiment

A ninth embodiment will explain a configuration wherein the wires arereplaced by lead plates in the third embodiment.

FIG. 37 shows an overall plan view illustrative of a main surface sideof a package 10F of the ninth embodiment as seen through the interior ofthe package 10F, FIG. 38 shows a sectional view taken along line Y5-Y5of FIG. 37, and FIG. 39 shows a sectional view taken along line X3-X3 ofFIG. 37, respectively. Incidentally, FIG. 37 shows lower semiconductorchips 5 a 2 and 5 b as seen through the lead plates to make it easy tosee the drawing. A p channel vertical power MOSQH2 is formed in thesemiconductor chip 5 a 2.

In the ninth embodiment, pads HSPs placed over a main surface of thesemiconductor chip 5 a 2 formed with a high-side power MOS, and leads 7b 1 for an input power supply VIN are electrically connected to oneanother by a lead plate 30 e. Pads LSPs for a source electrode, whichare placed over a main surface of the semiconductor chip 5 b formed witha low-side power MOS, and leads 7 b 2 for a reference potential GND areelectrically connected by a lead plate 30 f. The material for each ofthe lead plates 30 e and 30 f is identical to the leads 30 a through 30d. The lead plates 30 e and 30 f are disposed so as to cover themajority of the main surfaces of the semiconductor chips 5 a 2 and 5 bthat serve as heat generation sources in a manner similar to the leads30 a through 30 d. In the present embodiment, the lead plates 30 e and30 f are covered with an encapsulator 6 over their entirety.

According to the ninth embodiment, the parasitic inductances L2 and L5can be reduced by use of the lead plates 30 e and 30 f. Parasiticresistance can also be reduced as compared with the wires W. It is thuspossible to further reduce switching losses and conduction losses of anon-insulated DC-DC converter 1 and to further improve voltageconversion efficiency of the non-insulated DC-DC converter 1.

Tenth Preferred Embodiment

A tenth embodiment will explain a configuration wherein the lead platesof the ninth embodiment are exposed onto the surface of a package.

FIG. 40 shows an overall plan view illustrating an upper surface(corresponding to a surface opposite to a mounting surface of a package10G where the package 10G is mounted to a printed wiring board) of thepackage 10G according to the tenth embodiment, FIG. 41 shows a sectionalview taken along line Y5-Y5 of FIG. 40, and FIG. 42 shows a sectionalview taken along line X3-X3 of FIG. 40, respectively. Incidentally, aninternal plan view of the package 10G is identical to FIG. 37.

In the tenth embodiment, parts of lead plates 30 g and 30 h are exposedfrom the upper surface of the package 10G. Thus, radiation can beenhanced. Allowing the lead plates 30 g and 30 h to have a radiatingfunction makes it unnecessary to add other parts for radiation.Therefore, the process of assembling a semiconductor device can besimplified as compared with the addition of the radiating parts, and thetime required to assemble the semiconductor device can be shortened.Since the number of parts can be reduced, the cost of the semiconductordevice can be cut down. Incidentally, the material for the lead plates30 g and 30 h and their plane shapes are respectively identical to thelead plates 30 e and 30 f.

Depressions (chamfered portions) 32 are provided on the upper outerperipheries of the lead plates 30 g and 30 h in a manner similar to thesixth embodiment, thereby making it possible to improve the strength ofbonding between the lead plates 30 g and 30 h and an encapsulator 6. Itis therefore possible to suppress or prevent a defective condition thatthe lead plates 30 g and 30 h come off. The depressions 32 may beprovided on the lower outer peripheries (on the sides nearersemiconductor chips 5 a 2 and 5 b) of the lead plates 30 g and 30 h.Configurations other than these are identical to those in the third andninth embodiments. Incidentally, the structure of the tenth embodimentcan be applied even to the case in which a high-side power MOS of thesemiconductor chip 5 a 2 is formed of an n channel horizontal power MOS.In such a case, the lead plate 30 g is connected to drain electrode padsHDPs disposed over a main surface of the semiconductor chip 5 a 2 via ajunction layer 31.

FIG. 43 shows a sectional view illustrating one example of aconfiguration wherein a radiating fin (heat sink) 33 is bonded onto theupper surface of the package 10G shown in FIGS. 40 through 42 via anadhesive 34 interposed therebetween. Bonding such a radiating fin 33thereto enables further enhancement of radiation.

Eleventh Preferred Embodiment

An eleventh embodiment will explain a configuration wherein an inputcapacitor Cin is mounted onto the package 10G of the tenth embodiment.

FIG. 44 shows an overall plan view illustrating an upper surface(corresponding to a surface opposite to a mounting surface of thepackage 10G where the package 10G is mounted to a printed wiring board)of the package 10G of the eleventh embodiment, FIG. 45 shows an overallplan view illustrating a main surface side of the package 10G as seenthrough the interior of the package shown in FIG. 44, and FIG. 46 showsa sectional view taken along line Y5-Y5 of each of FIGS. 44 and 45,respectively. Incidentally, a sectional view taken along line X3-X3 ofeach of FIGS. 44 and 45 is identical to FIG. 42.

In the eleventh embodiment, the input capacitor Cin is directly mountedover the upper surface of the package 10G in a manner similar to theseventh embodiment. That is, when the input capacitor Cin is seen in theplane, the input capacitor Cin is disposed in such a way that some ofthe input capacitor Cin are superimposed on both of semiconductor chips5 a 2 and 5 b. In this configuration, a lead plate 30 g is connected toan input power supply VIN, whereas a lead plate 30 h is connected to aground potential GND. Therefore, the input capacitor Cin can directly bemounted over upper surfaces from which the two lead plates 30 g and 30 hare exposed, so as to act as a bridge between the lead plates 30 a and30 h in the package 10G. Since the input capacitor Cin is exposed to theoutside even in the eleventh embodiment, this is suitable fordissipating heat generated in the input capacitor Cin per se.

One of a pair of electrodes 35 a of the input capacitor Cin is bondedand electrically connected to the lead plate 30 g via a junction layer36 interposed therebetween, whereas the other thereof is bonded andelectrically connected to the lead plate 30 h via the junction layer 36interposed therebetween. With the existence of the lead plates 30 g and30 h, flatness and sufficient connecting areas can be ensured forconnecting surfaces of the pair of electrodes 35 a of the inputcapacitor Cin. Therefore, connection ease and reliability of the inputcapacitor Cin can be improved. Incidentally, the material for thejunction layers 31 and 36 is identical to one described in the seventhembodiment. The configuration of the input capacitor Cin is alsoidentical to one described in FIG. 35.

Thus, in the eleventh embodiment, the input capacitor Cin can directlybe mounted onto the upper surface of the package 10G. The inputcapacitor Cin can be disposed in a near position directly above each ofthe semiconductor chips 5 a 2 and 5 b. Therefore, the parasiticinductances L1 and L6 can be reduced and the efficiency of power supplycan be improved. That is, since all the parasitic inductances L1 throughL6 can be reduced in the configuration having the three semiconductorchips 5 a 2, 5 b and 5 c in the package 10G of the eleventh embodiment,switching losses of a non-insulated DC-DC converter 1 can be reduced andan improvement in the efficiency of a system is made possible.

In a manner similar to the case described in the seventh embodiment, auser is able to select, according to the configuration of the entiresystem of the non-insulated DC-DC converter 1, a case in which theradiating fin 33 is mounted over the upper surface of the package 10G asshown in FIG. 43 illustrative of the tenth embodiment and a case inwhich the input capacitor Cin is mounted over the upper surface of thepackage 10G as described in the eleventh embodiment. When it is desiredto reduce the on resistance of the system, for example, the radiatingfin 33 may preferably be mounted. On the other hand, when it is desiredto reduce the switching losses of the system, for example, the inputcapacitor Cin may preferably be mounted.

FIG. 47 is one example of a configuration of a package 10H in which aninput capacitor Cin is contained therein, and shows a sectional viewillustrative of a spot corresponding to line Y5-Y5 of each of FIGS. 44and 45. A plan view of the package 10H is identical to FIGS. 44 and 45.While the input capacitor Cin is connected to lead plates 30 e and 30 fthrough a junction layer 36 interposed therebetween in the presentembodiment in a manner similar to FIGS. 44 and 45, the input capacitorCin is accommodated in an encapsulator 6. In this case, the presentembodiment can obtain the advantages that it is not necessary for a userto mount the input capacitor Cin, and extra efforts are not taken uponpackaging. Since such a configuration as not to expose the lead plates30 e and 30 f is taken, the fabrication of the package 10H is easy.

Next, FIG. 48 shows a plan view illustrative of one example of a mountedstate of the package 100 or the like, and FIG. 49 shows a side view ofthe package 10G or the like shown in FIG. 48, respectively.Incidentally, FIG. 48 is shown as seen through the package 10G in such away that the manner of wiring of a wiring board 37 is understood.

The wiring board 37 is constituted of, for example, a printed wiringboard. The packages 10G, 38 and 39 and chip parts 40 a and 40 b aremounted over its main surface. The control circuit 2 is formed in thepackage 38, and the load circuit 4 is formed in the package 39. The coilL is formed in the chip part 40 a, and the output capacitor Cout isformed in each chip part 40 b. Leads 38 a of the package 38 areelectrically connected to their corresponding leads 7 b (7 b 4) of thepackage 10G through wirings 37 a of the wiring board 37. Leads 7 b 1 ofthe package 10G are electrically connected to a wiring 37 b of thewiring board 37. Output leads (output terminals) 7 b 3 of the package10G are electrically connected to one end of a coil L of the chip part40 a through a wiring (output wiring) 37 c of the wiring board 37. Theother end of the coil L of the chip part 40 a is electrically connectedto the load circuit 4 through a wiring (output wiring) 37 d of thewiring board 37. Leads 7 b 2 for a reference potential GND, of thepackage 10G are electrically connected to one ends of the outputcapacitors Cout of the plural chip parts 40 b through a wiring 37 e ofthe wiring board 37. The other ends of the output capacitors Cout of thechip parts 40 b are electrically connected to the load circuit 4 throughthe wiring 37 d of the wiring board 37.

Next, FIG. 50 shows one example of a circuit system configuration of thenon-insulated DC-DC converter 1 containing the package 10G of theeleventh embodiment. In the circuit system, a plurality of packages 10Gare connected in parallel with one load circuit 4. An input power supplypotential Vin, a reference potential GND and a control circuit 2 areshared among the plural packages 10G. When such a configuration thatpower MOSQH2 and MOSQL1 and a driver circuit 3 are respectively packagedin discrete form is taken in such a circuit system, miniaturization ofthe entire system is impaired. On the other hand, since the power MOSQH2and MOSQL1 and the driver circuit 3 are accommodated in the same package10G in the eleventh embodiment, the entire system can be reduced insize. Incidentally, symbol Ds indicates the SBD referred to above.

One example of a method for assembling the package according to thepresent embodiment will next be explained using an assembly flow diagramshown in FIG. 51.

A lead frame and die bond paste are first prepared (Step 100). FIG. 52shows one example of a fragmentary plan view illustrative of unitregions or areas of the lead frame 7. FIG. 52 shows a main surface(semiconductor chip mounting surface) of the lead frame 7. The leadframe 7 has two frame-body sections 7 f 1 extending along the horizontaldirection (first direction X) of FIG. 52, a frame-body section 7 f 2extending in the direction (second direction Y) orthogonal to theframe-body sections 7 f 1 so as to act as a bridge between the twoframe-body sections 7 f 1, a plurality of leads 7 b extending from theinner peripheries of the frame-body sections 7 f 1 and 7 f 2 to thecenters of the unit areas, and two die pads 7 a 3 and 7 a 5 and anL-shaped wiring section 7 c formed integrally with the plural leads 7 band supported by the frame-body sections 7 f 1 and 7 f 2 through theleads 7 b. Half etching areas are formed on the outer peripheries on theback surface sides of the leads 7 b, die pads 7 a 3 and 7 a 5 and wiringsection 7 c and made thinner than other portions. Incidentally, forinstance, silver (Ag) paste was used as the die bond paste.

Subsequently, as shown in FIG. 53, the semiconductor chips 5 a 2, 5 band 5 c are mounted over the main surfaces of the die pads 7 a 3 and 7 a5 in the respective unit areas of the lead frame 7 through the die bondpaste. Thereafter, heat treatment is made to cure the die bond paste,thereby fixedly securing semiconductor chips 5 a 2, 5 b and 5 c onto thedie pads 7 a 3 and 7 a 5 (Steps 101 and 102). An improvement inproductivity can also be attained by mounting the semiconductor chips 5c, 5 a 2 and 5 b in small order. Incidentally, the semiconductor chips 5a 2, 5 b and 5 c are obtained by forming semiconductor chips 5 a 2, 5 band 5 c in their corresponding main surfaces of three types ofsemiconductor wafers through a normal wafer process (pre-process(including a device forming step and a wiring forming step)), thereafterbonding a dicing tape onto the back surfaces of the respectivesemiconductor wafers, and cutting out the corresponding semiconductorchips 5 a 1, 5 b and 5 c from the respective semiconductor wafer by adicing blade.

Subsequently, as shown in FIG. 54, lead plates 30 e and 30 f or leadplates 30 g and 30 h are connected as described above (Step 103).Thereafter, as shown in FIG. 55, bonding of thin wires WB is performed(Step 104). Since there is a fear that when the lead plates 30 e and 30f or like are connected after connection of the wires WB, break failuresof the wires WB are incurred upon connection of the lead plates 30 e and30 f or the like, the wires WB are connected after the process ofconnecting the lead plates 30 e and 30 f or the like. It is thuspossible to suppress or prevent the break failures of the thin wires WB.Thereafter, when the lead plates 30 e and 30 f are used, the inputcapacitor Cin may be connected to the lead plates 30 e and 30 f as inthe package 10H (Step 200).

Subsequently, as shown in FIG. 56, a resin sealing (mold) process isperformed by a transfer mold method (Step 105). The transfer mold methodis a method for using a pot, a runner, a resin implantation gate and amold die provided with a cavity and the like, and injecting athermosetting resin into the cavity from the pot via the runner andresin implantation gate to thereby form an encapsulator 6. Uponmanufacture of a QFN type package, an individual type transfer moldmethod for using a multicavity lead frame having a plurality of productforming areas (device forming area and product acquisition areas) andresin-sealing semiconductor chips mounted onto the respective productforming areas every product forming areas, and a batch-type transfermold method for collectively resin-sealing semiconductor chips mountedonto respective product forming areas are adopted. While FIG. 56illustrates by way of example, a case in which lead plates 30 g and 30 hare used, the lead plates 30 e and 30 f and the entire input capacitorCin are covered with the encapsulator 6 where the lead plates 30 e and30 f are used and the input capacitor Cin is connected in Step 200.

After the above resin sealing process, the injected sealing resin iscured (resin cure step 106). After the application of each mark (Step107), individual product portions are cut out from the lead frame 7 asshown in FIG. 57 (Step 108). After the resin sealing process and beforethe cutting step 108, the input capacitor Cin may be connected to thelead plates 30 g and 30 h as described above (Step 201). After thecutting step 108, the input capacitor Cin may be connected to the leadplates 30 g and 30 h as mentioned above (Step 109). The correspondingpackage 10G is manufactured in this way.

Twelfth Preferred Embodiment

A twelfth embodiment will explain a configuration wherein an inputcapacitor is directly connected to semiconductor chips.

FIG. 58 shows an overall plan view illustrative of a mina surface sideof a package 10 i of the twelfth embodiment as seen through the interiorof the package 10 i, FIG. 59 shows a sectional view taken along lineY7-Y7 of FIG. 58, and FIG. 60 shows a circuit diagram of FIG. 58,respectively. Incidentally, although FIG. 60 shows an example in which ap channel vertical power MOS is used as a high-side power MOS, an nchannel horizontal power MOS may be used.

In the twelfth embodiment, a pair of electrodes 35 a of an inputcapacitor Cin is directly connected via a junction layer 36 to pads(pads HSPs for a source electrode where a p channel vertical powerMOSQH2 is formed in a semiconductor chip 5 a 2, and pads HDPs for adrain electrode where an n channel horizontal power MOSQH3 is formed inthe semiconductor chip 5 a 2) placed over a main surface of thesemiconductor chip 5 a 2, and pads LSPs for a source electrode, whichare disposed over the main surface of a semiconductor chip 5 b. Sincethe parasitic inductances L2 and L5 used as the wire bonding sections inFIG. 1 cease to act parasitic inductances of a main circuit as shown inFIG. 60 in the twelfth embodiment, there is no need to wire using thelead plates 30 a, 30 b, 30 c and 30 d. Therefore, the cost of thepackage 10 i can be reduced. However, the sections where the electrodes35 a of the input capacitor Cin are connected at the main surfaces ofthe semiconductor chips 5 a 2 and 5 b, must eliminate the gate fingers12 b from the viewpoint of ensuring of connectivity and the gateresistance increases correspondingly. Therefore, the present embodimentis suitable for an apparatus driven at a low frequency and low currentas compared with the first and second embodiments. Configurations otherthan those are identical to the first and second embodiments.

Thirteenth Preferred Embodiment

A thirteenth embodiment will explain a configuration wherein the inputcapacitor is directly connected to semiconductor chips in the thirdembodiment.

FIG. 61 shows an overall plan view illustrating a main surface side of apackage 10 j of the thirteenth embodiment as seen through the interiorof the package 10 j, and FIG. 62 shows a sectional view taken along lineY5-Y5 of FIG. 61, respectively. Incidentally, a circuit diagram thereofis identical to FIG. 35. A sectional view taken along line X3-X3 of FIG.61 is identical to FIG. 23. Further, although FIG. 61 illustrates anexample in which a p channel vertical power MOS is used as a high-sidepower MOS, an n channel horizontal power MOS may be used.

Even in the case of the thirteenth embodiment, a pair of electrodes 35 aof an input capacitor Cin is directly connected via a junction layer 36to pads (pads HSPs for a source electrode where a p channel verticalpower MOSQH2 is formed in a semiconductor chip 5 a 2, and pads HDPs fora drain electrode where an n channel horizontal power MOSQH3 is formedin the semiconductor chip 5 a 2) placed over a main surface of thesemiconductor chip 5 a 2, and pads LSPs for a source electrode, whichare disposed over the main surface of a semiconductor chip 5 b. Thus,since the circuit diagram results in the circuit shown in FIG. 35, theparasitic inductance can be reduced at low cost in a manner similar tothe twelfth embodiment. Since, in this case, the number of wires WA1must be reduced in addition to the elimination of the gate fingers 12 b,the gate resistance further increases. Thus, the present embodimentincreases in loss as compared with the first and second embodimentswhere driven at a high frequency and large current. However, when thepresent embodiment is driven at a low frequency and low current, theloss remains unchanged so much as compared with the first and secondembodiments, and a reduction in cost can be realized. Since, however,the proportion or rate of conduction losses of the high-side power MOSis not so large, the package 10 j having the configuration of thethirteenth embodiment and the packages 10G and 10H shown in FIGS. 46 and47 may be used properly depending upon use conditions of the system anduser's desires.

Fourteenth Preferred Embodiment

A fourteenth embodiment will explain a configuration wherein in apackage with an input capacitor built therein, a back surface thereofopposite to a main surface from which die pads are exposed, is used as apackage mounting surface.

FIG. 63 shows a sectional view of a package 10 k of the fourteenthembodiment. Incidentally, a plan view thereof is identical to FIG. 45.FIG. 63 is a sectional view taken along line Y5-Y5 of FIG. 45.

A structure of the package 10 k according to the present embodiment issubstantially identical to one shown in FIG. 47. The present embodimentis different therefrom in the following points.

First, leads 7 b (7 b 1 and 7 b 2) are bent from a main surface fromwhich a die pad 7 a 5 of the package 10 k is exposed, to the side of theback surface of the package 10 k, which is placed on the side oppositeto the main surface. Thus, the area where the leads 7 b and anencapsulator 6 contact can be increased, and adhesion power between theleads 7 b and the encapsulator 6 can be enhanced. It is thereforepossible to suppress or prevent a defective condition that the leads 7 bfall off the encapsulator 6.

The second point is that the leads 7 b (7 b 1 and 7 b 2) are exposedfrom the main surface, back surface and side faces of the package 10 k,and the back surface placed on the side opposite to the exposed surfaceof the die pad 7 a 5 of the package 10 k is configured as the mountingsurface of the package 10 k. Thus, since radiation from both of the mainsurface of the package 10 k and the back surface thereof is allowed, aheat dissipation property can be improved as compared with the firstembodiment. FIG. 64 shows a sectional view illustrating a state in whicha package 10 k is mounted onto a wiring board 37 and a radiating fin 33is attached. The package 10 k is mounted over the wiring board 37 in astate in which leads 7 b (7 b 1 and 7 b 2) thereof are connected totheir corresponding wirings 37 b and 37 e of the wiring board 37 via ajunction layer 42. The junction layer 42 comprises, for example,tin-silver lead-free (unleaded) solder (melting point: about 221°) likea tin-silver (Ag)-copper (Cu) alloy, a tin-silver-bismuth (Bi)-copperalloy or the like, tin-copper lead-free solder (melting point: about227°) like a tin-copper-nickel (Ni) alloy or the like, tin-zinclead-free solder (melting point: about 198°) like a tin-zinc (Zn) alloyor the like, tin-bismuth lead-free solder (melting point: about 148°)like a tin-bismuth-silver alloy or the like, or lead-free solder like atin-stibium (Sb) alloy.

In the case of such a structure according to the present embodiment, theradiating fin 33 can be provided over the main surface (surface fromwhich some of the die pad 7 a 3 and 7 a 5 and leads 7 b (7 b 1 and 7 b2) are exposed) of the package 10 k via an adhesive 34 interposedtherebetween. That is, it is possible to cause heat generated at thesemiconductor chips 5 a 2, 5 b and 5 c to escape to the outside throughthe die pads 7 a 3 and 7 a 5 and the radiating fin 33. Namely, in thepresent embodiment, the heat can be radiated form both faces of thepackage 10 k. Further, since the radiating fin 33 is attached to themain surface of the package 10 k, the on resistance of the system can bereduced with a further improvement in dissipation, and the inputcapacitor Cin can be connected close to the semiconductor chips 5 a 2and 5 b. Hence switching losses of the system can also be reduced.

Fifteenth Preferred Embodiment

A fifteenth embodiment will explain a configuration wherein in a packageexternally provided with an input capacitor, a back surface opposite toa main surface from which die pads are exposed is formed as a mountingsurface of the package.

FIG. 65 shows a sectional view illustrating a state in which a package10 m of the fifteenth embodiment is mounted onto a wiring board 37 and aradiating fin 33 is attached, and FIG. 66 shows a fragmentary plan viewof FIG. 65 as viewed from the back surface side of the wiring board 37,respectively. Incidentally, a cross-section taken along line Y8-Y8 ofFIG. 66 corresponds to FIG. 65.

A structure of the package 10 m according to the fifteenth embodiment issubstantially identical to one shown in FIG. 46. The present embodimentis different therefrom in the following points, for example.

First, leads 7 b (7 b 1 and 7 b 2) are bent from a main surface fromwhich a die pad 7 a 5 of the package 10 m is exposed, to the side of theback surface of the package 10 m, which is placed on the side oppositeto the main surface, in a manner similar to the fourteenth embodiment.Thus, the area where the leads 7 b and an encapsulator 6 contact can beincreased, and adhesion power between the leads 7 b and the encapsulator6 can be enhanced. It is therefore possible to suppress or prevent adefective condition that the leads 7 b fall off the encapsulator 6.

The second point is that the leads 7 b (7 b 1 and 7 b 2) are exposedfrom the main surface, back surface and side faces of the package 10 m,and the back surface placed on the side opposite to the exposed surfaceof the die pad 7 a 5 of the package 10 m is configured as the mountingsurface of the package 10 m.

Even in the case of the fifteenth embodiment, the package 10 m ismounted over the wiring board 37 in a state in which the leads 7 b (7 b1 and 7 b 2) thereof are connected to their corresponding wirings 37 band 37 e of the wiring board 37 via a junction layer 42. Even in thefifteenth embodiment as well, the radiating fin 33 can be provided overthe main surface (surface from which some of the die pad 7 a 3 and 7 a 5and leads 7 b (7 b 1 and 7 b 2) are exposed) of the package 10 m via anadhesive 34 interposed therebetween. That is, it is possible to causeheat generated at the semiconductor chips 5 a 2, 5 b and 5 c to escapeto the outside through the die pads 7 a 3 and 7 a 5 and the radiatingfin 33.

In the fifteenth embodiment, lead plates 30 g and 30 h are bonded toconductor patterns 37 g placed over the main surface (mounted surface)of the wiring board 37 through junction layers 42. Further, they areconnected to conductor patterns 37 i placed over the back surface of thewiring board 37 through conductor portions 37 h lying in a plurality ofthrough holes. That is, since it is possible to cause heat generated atthe semiconductor chips 5 a 2, 5 b and 5 c to escape to the outsidethrough the lead plates 30 g and 30 h, the conductor patterns 37 g, theplural conductor portions 37 h and the conductor patterns 37 i, afurther improvement in radiation can be enhanced.

Such an aperture or opening 37 j as to expose parts of the lead plates30 g and 30 h placed over the mounting surface of the package 10 m isdefined in the wiring board 37. An input capacitor Cin is mounted in theopening 37 j.

Thus, since heat can be radiated from the radiating fin 33 and theconductor patterns 37 i in the fifteenth embodiment, a furtherimprovement in heat dissipation property can be improved. Since the onresistance of the system can be reduced and the input capacitor Cin canbe connected close to the semiconductor chips 5 a 2 and 5 b, switchinglosses of the system can also be reduced.

While the invention made above by the present inventors has beendescribed specifically on the basis of the preferred embodiments, thepresent invention is not limited to the embodiments referred to above.It is needless to say that various changes can be made thereto withinthe scope not departing from the gist thereof.

Although the flat package structure has been illustrated as the packagestructure by way of example in the embodiment, for example, the presentinvention is not limited to it. For instance, a BGA (Ball Grid Array)package structure may be adopted.

While the above description has principally been made of the case inwhich the invention made by the present inventors is applied to a drivepower supply circuit for each of a CPU and a DSP, which belongs to thefield of application reaching the background of the invention, thepresent invention is not limited to it but applicable in various ways.The present invention can be applied even to, for example, a powersupply circuit for driving of other circuit.

The present invention is applicable to the manufacturing industry of asemiconductor device.

What is claimed is:
 1. A semiconductor device comprising: a firstsemiconductor chip which includes a first MOSFET including a source, agate and a drain; a second semiconductor chip which includes a secondMOSFET including a source, a gate and a drain; a third semiconductorchip which includes a driver circuit for driving a gate of the firstMOSFET and a gate of the second MOSFET; a resin encapsulatorencapsulating the first, second and third semiconductor chips; an inputpower supply terminal exposed from the resin encapsulator and configuredto be used for supplying an input power; a reference potential supplyterminal exposed from the resin encapsulator and configured to be usedfor supplying a reference potential; and an output terminal exposed fromthe resin encapsulator and configured to be used for outputting anoutput, wherein a source-to-drain path of the first MOSFET iselectrically coupled in series between the input power supply terminaland the output terminal, wherein a source-to-drain path of the secondMOSFET is electrically coupled in series between the reference potentialsupply terminal and the output terminal, and wherein the firstsemiconductor chip and the second semiconductor chip are electricallyand mechanically coupled to a metal material which is electricallycoupled to the output terminal.
 2. A semiconductor device according toclaim 1, wherein the metal material is comprised of copper.
 3. Asemiconductor device according to claim 1, wherein the firstsemiconductor chip and the second semiconductor chip are coupled to themetal material via paste.
 4. A semiconductor device according to claim1, wherein the resin encapsulator has a top surface and a bottom surfaceopposite the top surface, and wherein the input power supply terminal,the reference potential supply terminal and the output terminal areexposed from the bottom surface of the resin body.
 5. A semiconductordevice according to claim 4, wherein the first semiconductor chipincludes a source electrode pad which is electrically coupled to thesource of the first MOSFET, and wherein the source electrode pad facestoward the top surface of the resin encapsulator.
 6. A semiconductordevice according to claim 1, wherein the second semiconductor chipincludes a drain electrode which is electrically coupled to the drain ofthe second MOSFET, and wherein the drain electrode is mechanicallycoupled to the metal material.
 7. A semiconductor device according toclaim 1, wherein the gate of the first MOSFET is electrically coupled tothe driver circuit via a first wire, and wherein the gate of the secondMOSFET is electrically coupled to the driver circuit via a second wire.8. A semiconductor device according to claim 7, wherein the firstsemiconductor chip has a rectangular shape in plan view, with a pair oflong sides and a pair of short sides, and wherein the first wire isdisposed so as to overlap one of the short sides of the firstsemiconductor chip.
 9. A semiconductor device according to claim 1,wherein the first semiconductor chip has a rectangular shape in planview, with a pair of long sides and a pair of short sides, and whereinone of said long sides of the first semiconductor chip is arranged suchthat a closest distance between the second semiconductor chip and saidone long side is less than a closest distance between the secondsemiconductor chip and the other long side.
 10. A semiconductor devicecomprising: a first semiconductor chip which includes a first MOSFETincluding a source, a gate and a drain; a second semiconductor chipwhich includes a second MOSFET including a source, a gate and a drain; athird semiconductor chip which includes a driver circuit for driving agate of the first MOSFET and a gate of the second MOSFET; a resinencapsulator encapsulating the first, second and third semiconductorchips; an input power supply terminal exposed from the resinencapsulator and configured to be used for supplying an input power; areference potential supply terminal exposed from the resin encapsulatorand configured to be used for supplying a reference potential; an outputterminal exposed from the resin encapsulator and configured to be usedfor outputting an output; wherein a source-to-drain path of the firstMOSFET is electrically coupled in series between the input power supplyterminal and the output terminal, wherein a source-to-drain path of thesecond MOSFET is electrically coupled in series between the referencepotential supply terminal and the output terminal, and wherein the firstsemiconductor chip and the second semiconductor chip are electricallyand mechanically coupled to a metal material which is electricallycoupled to the output terminal.
 11. A semiconductor device according toclaim 8, wherein the metal material is comprised of copper.
 12. Asemiconductor device according to claim 8, wherein the first MOSFETcomprises a p channel MOSFET, and wherein the second MOSFET comprises ann channel MOSFET.
 13. A semiconductor device according to claim 8,wherein the first MOSFET includes a first drain electrode which iselectrically coupled to the drain of the first semiconductor chip,wherein the second MOSFET includes a second drain electrode which iselectrically coupled to the drain of the second semiconductor chip, andwherein the first and second drain electrodes are mechanically coupledto the metal material.
 14. A semiconductor device according to claim 8,wherein the resin encapsulator includes a top surface and a bottomsurface opposite the top surface, and wherein the input power supplyterminal, the reference potential supply terminal and the outputterminal are exposed from the bottom surface of the resin body.
 15. Asemiconductor device according to claim 14, wherein the first MOSFETincludes a first source electrode pad which is electrically coupled tothe source of the first semiconductor chip, wherein the second MOSFETincludes a second source electrode pad which is electrically coupled tothe source of the second semiconductor chip, and wherein the first andsecond source electrode pads faces toward the top surface of the resinencapsulator.